Abstract: Rule of urban land expansion and cultivated land occuption was analyzed based on interpretation of remote sensing image data in 1975, 1987, 1995, 2000 and 2005. Urban land expansion was conducted a quantitative analysis with urban land expansion intension, urban land expansion core, urban land expansion type, compact degree of urban land expansion and urban land expansion fractal index theoretical model. Spatial analysis of expansion track in different buffer scales was conducted by buffer analysis method. The results showed that Chongqing urban district and Yubei district were occupied a large number of culitivated land. Near the districts affected by expansion core of Chongqing urban district and Yubei district were higher expansion intension. The expansion was order and the expansion model was filling. Buffer analysis was an effective method in the research of urban expansion track. The urban expansion intension was higher in the second buffer strand of the study area. Analysis of the urban expansion encroachment onto cultivated land and its expansion spatial model in 1975－2005, which is help for controlling urbanization encroachment onto cultivated land , grasping urbanization stages and predicting the development trend in the future.