Abstract: Begins with analyzing the effect of nonsmooth vector field of a piecewise-linear system on the differentiability of the Poincare mapping, then, presents the dynamics complexity of the system through numerical simulations. The study shows that the system differs greatly in dynamics from a system with smooth vector field, when its periodic motion approaches a bifurcation of saddle-node(or relevant degenerated)type or penetrates a switching plane between two linear regions at very low velocity.