Abstract: The stability and resistance to pressure of piston sub-mini underwater vehicle are analyzed in this paper. Mechanical structure and experimental platform are introduced first. The unique ups and downs control mechanism with piston is used to control the motion of underwater vehicle in vertical direction. Ups and downs control is one of the main controls of underwater vehicle, so theory design, underwater experiment and finite element analysis are made separately to further verify the reliability and availability of the design. Experimental results suggest that the design is reasonable, feasible and practical.