Abstract: A differential equation is derived for the vibration of vehicle's suspension system involving damping. Then, the transfer function is solved analytically through the solution to linear equation set with undetermined coefficients after Laplace transform, and the amplitude is solved by way of inverse Laplace transform. After an in-depth discussion on the Laplace transform and analytic solution as above, it is found that the transform is selective so that another analytic solution is available, which will be easier to express and analyze. Regarding the road pavement spectrum as the superposition of lots of sine functions and assuming that the vehicle is traveling steadily, an effective and simple analytic expression of amplitude is given based on the linear system additivity for outputs, thus avoiding the trouble with a series of solutions. In this way, the moving load on active suspension is given numerically, and the algorithm has been implemented with VB programming. The software developed therefore provides a preparation for the dynamic reliability design/analysis of suspension.