Abstract：Based on influence coefficient method and principle of conversation of potential, stiffness mapping of Stewart mechanism is established, which takes into account the elastic deformation of active, passive joints and the effect of external wrench. Compared with the prevalent stiffness mapping model, the proposed model is more general and exact, not only considering the axis stiffness of actuator, but also considering the stiffness of passive joints and the change of Jacobian matrix brought about by tiny change of mechanism under external wrench. An example is analyzed combining stiffness matrix Reyleigh quotient to contrast the stiffness performance differences between the two models.