Abstract: To verify mechanical self-adaptability of drive unit of the tri-axial differential in-pipe robot,and to deeply analyze the transmission principle of the tri-axis differential drive unit,an experimental system of robot self-adaptability is developed,which includes tri-axis differential drive unit,simulated operating environment and performance test system.With the goal of quantitatively evaluating the performance of tri-axis differential drive unit,a performance index set is established to evaluate objectively the performance of a new type of tri-axis differential drive unit.Experimental studies show that the triaxis differential drive unit of in-pipe robot has good mechanical self-adaptability to various changes in geometric constraints of pipe environment.