The study carries out optimal design for the cam profile of the valve train in a high-specific-power diesel engine. The dynamic analysis on the original cam reveals that the original one, which leads to adequate fullness coefficient, is designed far from the material margins. The fullness coefficient and time area value are selected as the optimization objective, and the piecewise fucntion method is utilized to optimally design the cam profile. The restrictive contidons are applied to each section on the cam. Thus the function and the optimal coeficients are obtained. Then the dynamic analysis and working process simulation on the optimal valve train are carried out, and it proves that the dynamic and intake port performaces of the optimized one are greatly impoved.