This study investigated the selection of dens of three species of canids from March to June of 2005 in the prairie of eastern Inner Mongolia. 80 dens ,included 20 wolf dens、27 red fox dens and 33 corsac fox dens, were measured. Through principal component analysis, Independent-samples T Test and Chi-square statistic analysis, we found: The entrance direction has no significant difference among them. The angle of dens entrance, diameter of dens entrance and lenghth of the first chunnel has no significant difference between red fox and corsac fox also. But the angle of wolf dens entrance was less than others, and wolf dens has the biggest entrance.Wolves often locate their dens in dry reed pond of near the water source and far from human disturbance. Den sites are characterized by better Sheltering class and flattest slope. Result of principal component analysis showed that the first 3 principal components explained 83.080% of the total variance among all habitat variables. According to absolute value of coefficient, the 3 components were classified separately as sheltering class factor, disturbance factor and water factor. Sheltering class factor is the chief factor in den site selection.Red fox preferred to den in the flat willow bosk with better sheltering class, which far from human disturbance and near the water source. Result of principal component analysis showed that the first 3 principal components explained 80.659% of the total variance among all habitat variables. According to absolute value of coefficient, the 3 components were classified separately as landform factor, water factor and disturbance factor. Landform class factor is the chief factor in den site selection.Most of corsac fox dens locate in the top slope with high grass and far from human disturbance. The distance between den and water source is about 2200m. Density of rodent is high around corsac fox dens. Result of principal component analysis showed that the first 3 principal components explained 81.343% of the total variance among all habitat variables. According to absolute value of coefficient, the 3 components were classified separately as microclimate factor, disturbance factor and food factor. Microclimate factor class factor is the chief factor in den site selection.Better sheltering class and keeping away from human disturbance is common requirement of three species of canids. The main difference between corsac fox dens and others are the distance to water source and Slope location. Dry reed pond is the first option to wolf, red fox prefer to den in the flat willow bosk, and corsac fox like to breeding pups in Sloping field with high grass.The spatial nich of dens could be ranked in decreasing order of width as follows: wolf, red fox, corsac fox. The overlap of spatial niche between wolf and red fox is remarkable, and the overlap between red fox and corsac fox is inapparent.