The purpose of this study was to analyze the effects of soil depth on vegetation cover and above ground biomass of natural grasses protected from grazing in the east part of Inner Mongolia through field survey.The results show that when soil depth was under 20 cm,the vegetation cover and above ground biomass decreased sharply as the soil depth decreased.When soil depth was less than 10 cm,the vegetation types were different from that of normal vegetations,and the vegetation cover and above ground biomass were very low(less than 30% coverage and 150 g/m2);When soil depth was greater than 20 cm,the vegetation cover and above ground biomass were greater than 80% and 200 g/m2,and changed slowly as soil depth increased.The minimum soil depth in this area should be at least 20 cm for the natural grasses to grow healthily.