Abstract: In this article we have shown, if the wave packets are used to describe the dynamical states of particles in a many-particle system, we can get a set of Langevintype Eq. (4.1) instead of the classical canonical eqs. of Hamilton (1.1). At the same time a diffusion-type Liouville theorem involving quantum effect (4.9) is resulted instead of the classical Liouville Eq. (1.3). it is shown that the diffusion-type Liouville eq. should cause the phase mixing in phase space and the entropy increasing in time for an isolated system.