In this paper, the flexible effect of links and joints are considered based on the virtual spring method. From deriving the dynamic equations, we can obtain the forces and moments applied on links and joints, and the deflection can be calculated accordance with the stiffness matrix of virtual springs. We lump the link flexibility into each joints by using an equivalent stiffness method. As opposed to the rigid-body models, the angular position is used to model flexibility of the two neighboring links. This method is a great compromise, because it does not significantly increase the complexity of the formulation, yet it accounts for the link flexibility to some degrees.