The analysis calculation of meshing stiffness of helical gear is the basis for the study of gear dynamics. According to the gear meshing principle and coordinate transformation theory the finite element model of helical gear meshing with the installation error is established,a finite element calculation method of the meshing stiffness of helical gear considering the installation error is proposed. Put the installation error parameterized,by using the finite element software,the variation of meshing stiffness of helical gears is analyzed. The time- varying meshing stiffness is got by the way of using the quasi- static process simulation dynamic behavior,the variation law of the time- varying meshing stiffness under different installation errors are analyzed. The results show that the installation error decreasing the meshing stiffness,especially the angle deviation is more serious,and the influence of the angle deviation on the meshing stiffness has a certain rule. The effect of different installation error of the meshing stiffness is different,under a light load condition is obviously heavy.