Plasma microturbulence is well described by a kinetic equation coupled with Poisson equation for the turbulent potential. Here, taking the 2-dimensional (1 for space and 1 for the velocity space) Vlasov-Poisson equation as an example, we study the Landau damping and phase mixing using numerical simulations. A collision term is introduced to avoid the numerical recurrence in the phase space, and the effect of the collision is examined in detail.