Abstract: It is introduced that the derivation,types,characteristics,principles for the location of the bulbs and branches,comprehensively estimating method for ultimate bearing capacity,calculation formula of vertical compressional bearing capacity,calculation formula of compressive bearing capacity of shaft of DX pile and structure of DX extruding device.Through the static loading tests for 24 DX piles and 3 DX piles with large scale field model,where the reinforcement stress detectors or electrial resistance strain gauges were embedded,the regular patterns and characteristics of mechanisms of bearing capacity of DX piles are systemically studied,and the developments and the distributions of the skin-friction resistances,the bulb resistances and the tip resistances under ultimate and working conditions are detailedly analysed,the developments of the unit skin-friction resistances of each sections of DX piles and the unit bulb resistances and the unit tip resistances of DX piles are systemically studied.The differences of load transfer mechanisms between DX piles and uniform bored piles,and the differences of mechanisms between compressive and tensional DX piles are also comparatively analysed.Finally,how to guarantee the static loading test so that to obtain the full useful data of the mechanisms of bearing capacities also are indicated.