In Parameters of valve trains,such as cam profiles and valve timing,have very important influence on power output and economical efficiency of internal combustion engine.For increasing the torque of a domestic-produced diesel engine at low speed con-dition,it is analyzed in details the valve timing,the static and dynamic characteristics of cam profiles in the original roller-arm valve mechanism system.Comparing the parameters with the other same type diesel engines,three improved projects of cam are proposed and compared by simulation model which has been verified by experimental data.Both cam profiles of High-order Polynomial Functions type and Low-order Polynomial Combination Functions type are applied to the design process by using the self-developed cam design soft-ware.Several factors should be considered in the design process of engine valve trains,however,among which the valve timing and the fullness coefficients of cam profiles are the most two important factors.With the constraint condition of the fullness coefficients value of cam profiles must be bigger than 0.55 and the minimum value of negative curvature radius must be bigger than the radius of grinding wheel used during the manufacture process,the project of Low-order Polynomial Combination Functions type profiles are selected to be the optimized one.Through the engine test verification and validation,the torque of the optimized engine increases over 11%and the fu-el consumption decreases by 2.34%at low speed condition.