Based on bond graph theory,considering the time-varying meshing stiffness,damping and tooth surface friction force of internal and external gear,using LuGre friction model,the bond graph model of NGW type planetary gear was established. And then,the bond graph analysis models of the XP type and PX type single loop planetary transmission system were set up. The speed and efficiency of XP type and PX type single loop planetary transmission system was computed and simulated in 20 sim software. The results show that the modeling theory and method of bond graph can be used to solve the nonlinear dynamic problems of single loop planetary transmission system.