It is the aim of this presentation to deal with an improved transfer matrix method for three dimensional vibration analysis of a reciprocating engine crankshaft system, so as to provide an efficient and convenient method for complex crankshaft system dynamic analysis. For different type of crankshafts, only the numbers and relative direction angles of the cylinders are required as input data besides the structural data. The theoretically predicted frequencies and mode shape agree well with the experimental results. In the case of dealt with a four-cylinder two-stroke small engine, five times exciting forces are of the most important which induce the crankshaft resonance. An effective and convenient general computer program for disign engineer to operate has been developed.