Crankshaft is one of the main components in reciprocating mud pump (RMP). Its stress significantly affects reliability and performance of high pressure and large power RMP. In this study CAE stress analysis was actively applied to secure the high reliability of main components and improve the performance of RMP. Through movement analysis and computation for various components of RMP, the load of crankshaft was obtained. By effectively using CAE stress analysis to three kinds of dangerous working conditions of crankshaft, distribution characteristics of the max main stress, the min. main stress and the Mises stress were obtained. The most dangerous condition and position were gotten through stress analysis. The analysis results give theory support for design and development of high pressure, large power, high performance and high reliability RMP.