The physical property of karst mountain desertification soil under different land use in Chongqing Beipei karst mountain was studied. The result shows that when the nature forest land is replaced by grass land,artificial land, vegetable land and plantation gradually, the land is becoming more arenaceous and the soil bulk density in- creases, and the total percentage of pore, especial the percentage of non-pore increase greatly. Although the ag- gregate structure measured by dry sieve are quiet similar under different land use, the water-stable aggregate structure got by dump sieve is quite different. The destroy of aggregate structure is high. With the vegetable land and plantation changed into deserted land, all physical standards are improved. On the basis of those studies, the author briefly analyzed the correlation between the degrading soil physical feature and the desertification, and pos- sibility of reducing the soil erosion by deserting land.