Abstract: To improve the design of a reciprocating compressor, the Visual C++ and Pro/E were used to develop a system software for the digital analysis and design of crankshaft. The stress state of crankshaft was analyzed during a cycle period on the principle of both thermodynamics and dynamics. A limit-state equation was given for the critical sections according to the randomness of design parameters, such as geometric dimensions, machining process and material strength. Then, both the reliability of fatigue strength and the sensitivity of influencing parameters were discussed so as to implement the digital analysis via VC. And all the design parameters of the crankshaft, including dimensions, process technology and material, were thus determined to implement the digital design via Pro/E. The results showed that the digital system software combining reliability theory with modern computer technology is highly promising in engineering practice.