The stiffness model of Hooke joint in the parallel mechanism was constructed based on a specific Hooke joint. Attitude matrix of the Hooke hinge was constructed, the reverse solution of the posture in operation was analyzed, as well as for the relationship between posture and force. The stiffness matrix of toppedestal and bottompedestal were constructed on the Hooke joint, obtaining the equivalent axial stiffness of the branch chain of the parallel mechanism by the means of elastic potential energy equivalent principle and homogeneous transformation. The research results provide a certain basis for the stiffness modeling of Hooke joint in parallel mechanism.