For the difference of dynamic calculation between the single and the whole valve system, the dynamic models of valve mechanism were built based on the theory of multimass dynamics, the dynamic characteristics of two valve systems were compared, the influence of camshaft distortion on valve mechanism dynamics was analyzed, and the concrete reason causing the difference was finally summarized. The research shows that the camshaft of whole valve system undergoes torsion and bending under the coupling of various forces. The distortion then leads to the errors of valve phase, resulting in the uneven distribution of each valve system. Accordingly, the whole valve system is superior to the single valve system in reflecting the dynamic differences of valve mechanism.