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Exechon parallel kinematic machine (PKM) has been applied to machining, assembling and aerospace industries due to its high rigidity and high dynamics. However, its rotational ability is comparatively weak. In order to improve the rotational ability of the Exechon PKM, this paper proposed an Exevariant PKM whose topology is a 2R-P-U&1R-P-S parallel mechanism. And the mechanical structure of the proposed PKM was designed. According to its structure features, Exevariant PKM was divided into several subsystems. By considering the compliances of joints and limb structures and using the substructure synthesis technique, an analytical stiffness model was developed for performance evaluation. The stiffness matrix of the platform was derived to demonstrate a positiondependency. The stiffness matrix of the Exevariant PKM at the extreme configuration was computed to show a coupling effect in the PKM’s stiffness characteristics. Deformation of the Exechon PKM under an external load was computed by ANSYS workbench, based on calculation errors between the finite element method and the proposed analytical method which were obtained to illustrate the high accuracy of the analytical model. The proposed methodology of stiffness modeling can also be applied to other overconstrained PKMs and can evaluate the global rigidity over workplace efficiently with minor revisions.