Abstract: This paper briefly reviews the study of soil spatial variability. Based on the theory of geostatistics and the research experience in soil spatial variability, the problem of semi-variogram which is a key to study soil spatial variability was discussed，including its basic hypothesis, sampling, modeling and statistic test. Some suggestions were given for determining semi-variogram model，such as on the condition of satisfying sample size: checking the data whether they correspond to the intrinsic hypothesis: enhancing the confidence for every estimating point， choosing the safety model as semivariogram model and testing statistically to semi-variogram model.