Hydraulic confined piston engine (HCPE) is a new type power device which can directly turn indicated work into hydraulic power, and three cylinders axial HCPE prototype has been manufactured. The load and stress study on its crankshaft is very important for future design. The working principles of HCPE was discussed, the mathematic model of its working process was constructed, and the load on crankpin by connecting rod was obtained by simulation. The total contact model of crankshaft reflecting the actual conditions was built, through which Von Mises stress, contact stress and friction stress of crankshaft were calculated. The maximum of Von Mises stress occures at the fillets of main shaft neck. The fatigue secure coefficient of crankshaft is about 2.85, which meets the demand.