There is a wide range of industrial applications for the 4DOF parallel mechanism which can achieve SCARA type output motion (three dimensional translation and one dimensional rotation). A novel fourdegreeoffreedom highspeed parallel robot mechanism for SCARA was proposed, which consisted of two RSS branches and two R(SRS)2R branches. Firstly, the topological structure characteristics such as the POC set of moving platform and mobility were first obtained based on the design theory of position and orientation characteristic （POC） set. Secondly, the virtual spring method was used to establish the stiffness model of the branch and the static of the branch was given. The differential mapping of the virtual joint deformation to the end deformation in the branch was obtained by the spin method and the Cartesian stiffness matrix at the end of the mechanism was obtained according to the static equation. By means of a nondimensionalization of the stiffness matrix, the 6×6 inhomogeneous stiffness matrix was decomposed into two homogeneous submatrices, of which two performance indices, corresponding to the translational and rotational stiffnesses, were defined to evaluate the stiffness behaviors of the manipulators. And the stiffness index analysis of the mechanism was carried out, and the stiffness characteristics of the mechanism in different working planes were analyzed. In addition, the dynamic analysis of the mechanism was performed to solve the velocity and acceleration of the active pair, the passive pair and the moving platform of the mechanism. The dynamic equation of the mechanism was established by using the virtual work principle. Finally, the simulation was compared with the ADAMS threedimensional model simulation to verify the dynamics. The correctness of the modeling laid the foundation for further research and practical application of the organization.