With the release of the "Soil Pollution Prevention and Control Action Plan" (hereinafter referred to as "Soil 10"), many people in the industry believe that the soil testing market in China will have a huge market potential of 52 billion yuan in the next five years. Grasp the actual situation of soil pollution and risk control on the premise of the sampling representative and the accuracy of testing. However, during the investigation, the author found that in practice, the representativeness of soil sampling, sampling density and detection accuracy sometimes become the technical bottleneck of soil testing. In fact, the soil itself is a highly inhomogeneous medium with sampling errors far greater than analytical errors. A study of 1 mu of such a small change in the nature of the soil mass randomly selected nine sample points, were collected nine soil samples, analysis of soil available phosphorus content. The results showed that the variance between samples was 6 times of the parallel samples, 73 times the repeat of the instrument reading, indicating that the sampling error is much larger than the error of the instrument analysis. Similarly, in another case, an 8-meter × 8-meter grid was sampled on a field 40 meters long and 32 meters wide. Total nitrogen was analyzed for the 20 samples collected. The sampling error was much larger than the analysis error. Therefore, sampling problems in soil pollution research may become the bottleneck of the soil testing industry nowadays. For this reason, we need to talk about how soil sampling reduces errors. Soil is an open system. In ecosystems, soil is located in the heart of hydrosphere, atmosphere, lithosphere and biosphere. The soil ring itself is an open system, and the four layers of the existence of material and energy exchange. Part of the pollutants in the atmosphere and hydrosphere will enter the soil, causing soil pollution. Depending on the route of entry, pollutants such as heavy metals have very different spatial distributions. At the same time, the spatial distribution of pollutants is also significantly affected by perennial dominant wind direction. The scope and extent of point sources are affected by point sources Emissions, chimney height, topography, meteorological conditions. For water pollution, the linear distribution of pollution along the banks of the river is generally presented and is greatly affected by the terrain. Due to the soil has a larger adsorption capacity, into the rice fields, heavy metals in the field is very uneven. According to Japanese scientists, the concentration of cadmium, zinc and lead in a 54-meter-long field can be doubled, with cadmium concentrations of 2.02 mg / kg and 1.04 mg / kg respectively, and copper concentrations of 348 mg / kg-168 Mg / kg, respectively, zinc is 101 mg / kg ~ 53.1 mg / kg; and plots on both sides of the left and right values ​​are not the same. In our study in Taiwan, the concentration of cadmium in a 50-meter field water inlet can be as high as 7.0 mg / kg, while the outlet can be as low as 0.2 mg / kg with a difference of up to 35 times. If there is no more sampling, easy to mistakenly judge the field of pollution. In the atmosphere, water, soil and other environmental elements, only the soil is the most inhomogeneous medium. The soil is a heterogeneous loose porous system, but also a colloidal system, chemical system, biological system, or a redox system. Therefore, pollutants into the soil will occur after a variety of physical, chemical and biological processes and redistribution. Although the pollutants reaching the soil surface are mainly distributed on the surface of the soil, the heavy metals are mainly adsorbed by the clay minerals, and the subsequent distribution is affected by the distribution of clay minerals. Some studies have determined that the soil cadmium content of 0-15 cm soil layer is 5.0 mg / kg, but cadmium content is as high as 18 mg / kg if the clay fraction is isolated. Because cadmium is mainly adsorbed on the clay in the soil, the difference in the texture of the main soil when collecting the soil sample will have a significant impact. Therefore, in the process of farming, redistribution of soil particles is likely to cause soil heavy metal differentiation. Some Japanese scientists have shown that, after the rake field, due to the floating of soil clay and its subsequent deposition on the soil surface, the 3 cm soil layer in the paddy field can have more than double the heavy metal content of the soil layer beneath it. Therefore, sampling must be uniform sampling, otherwise easy to bring error. In the sampling process for heavy metal analysis, in addition to avoiding the contamination brought by the sampling tools and appliances, sampling methods (serpentine, diagonal, plum blossom, etc.) must be determined, sampled at multiple points (usually 5 points or above) Acquisition of mixed samples; single-point sampling must be uniform sampling from top to bottom. However, when sampling other organic pollutants, taking into account the nature of the pollutants (such as volatility and photodecomposition), various sampling strategies should be taken to ensure that sampling errors are minimized.