Water is a major limit factor for plant growth in arid area. Based on the ecological fitting theory, the thesis systematically analyzed the quantitative relationship between plant ecotype and groundwater depth as well as soil water content, according to the test data in sample area and the plant ecotypes in Horqin sandy land. Following results have been got: for plants of hygrophytes, mesophytes, mesoxerophytes and xerophytes, the changing range of groundwater depth is respectively 0.45～1.66 m, 0.95～2.20 m, 2.20～4.59 m, and 3.45～7.45 m; the range of surface soil water content of roots layer is respectively 2.70%～25.54%, 0.80%～13.32%, 0.41%～2.25% and 0.28%～0.44%; and the range of soil water content of roots layer is respectively 5.59%～54.80%, 3.59%～9.19%, 0.71%～3.59% and 0.16%～0.78%. Even though, some transition ranges still exist between hygrophytes and mesophytes, also between mesoxerophytes and xerophytes; the transition range of groundwater depth is respectively 0.95～1.66 m and 3.45～4.59 m, that of surface soil water content in roots layer is respectively 2.70%～13.32% and 0.41%～0.44%, and that of soil water content of roots layer is respectively 5.59%～9.19% and 0.71%～0.78%.