Impact and nonlinear dynamic behaviors of gear pair system with combining time varying stiffness and friction is developed. Firstly The phase plane is divided into three different part to construct the Poincare mapping structure of piecewise linear gear pair system. And then the influences of load parameters and initial values on the impact and nonlinear dynamic behaviors of gear pair system are analyzed in numerical method. The results show that: 1) with the increasing of constant load , the interval of off meshing and the impact velocity are decrease, and the gears has steady movement. The initial value of appearance of grazing bifurcation is increase, 2)inversely with the increasing of fluctuating component of load , impact velocity is increase and the interval of off meshing is decrease, and the gears has instability movement.