Redundantly actuated parallel manipulator (RAPM) has been proved to have comparative advantages of higher rigidity and higher payload over other parallel manipulators. This paper is to establish a sufficient accurate stiffness modelling to evaluate the stiffness of the 2UPR-2RPS RAPM. Firstly, the structure of the 2UPR-2RPS RAPM is briefly introduced, followed by some necessary kinematic definitions. Next, a stiffness modelling of 2UPR-2RPS is established by including the compliances of all joints and limb structures. And a reasonable index is constructed to evaluate the stiffness of the 2UPR-2RPS RAPM. Finally, a set of stiffness experiments is carried out to verify the effectiveness of the proposed stiffness modelling of the 2UPR-2RPS. The results indicate that the relative errors between the proposed stiffness modelling and the experimental value are less than 6%. This indicates that the proposed stiffness modelling possesses sufficient accuracy and thus can be used to analyze the stiffness of the 2UPR-SRPS RAPM.