Soil salinization is a worldwide ecological problem. In Tianjin coastal area, soil has long suffered from sea water and high mineralization diving, so salinization is widely distributed. Choosing Taiping Town of Tianjin coastal area as a typical soil salinization coastal area, the authors determined the correlation between main salt ions in the soil, carried out the random uniform thinning test for sampling points in the study area, and discussed the influence of different sampling densities on the interpolation results and the evaluation results of soil salinization. The results show that the farmland soil in Tianjin coastal area has mainly anions of Cl^-, and cations of Na⁺, and that the total Cl and Cl^- have good correlation with total salt in the soil. The authors extracted randomly a small number of samples to test total salt, and established an equation of total Cl and total salt, which could accurately calculate the total salt values for the whole samples. High-density sampling can improve the representation of the samples: when the sampling density is more than 4 points per square kilometers, the acceptance rate of the relative error is equal or greater than 80%; in addition, sampling density of evaluating salinization levels should not be less than 1 points per square kilometers.