For a 1.2 m Zerodur primary mirror, an effective primary mirror support system was proposed. A lateral support based on 6 sets of flexible tangent link structures and an axial support based on 18 sets of semi-flexible Whiffletree structures were combined to ensure the primary mirror to maintain good surface figure accuracy and system stiffness at a larger temperature range and different elevation angles. The working principle of the system was analyzed and the surface figure accuracy of the primary mirror and modal of the support were tested. The analysis for system structure indicates that the support system ensures the positioning accuracy and surface figure accuracy of the primary mirror and its thermal decoupling ability is verified by support principle deduction. The finite element analysis (FEA)on the statics distortion and thermal distortion of the mirror surface shows that the system has excellent structural rigidity. The surface figure accuracy tests indicate that the RMS values of mirror optical surface distortion at the optical axis in vertical and horizontal states are 15.25nm and 20.75 nm respectively. Furthermore, the first natural frequency of support system is measured to be 60.3 Hz at modal tests. As comparing FEA simulation results with measurement results.It shows that relative errors of the mirror optical surface distortion are 14.0% and 17.8% separately at different elevation angles, and that of the first natural frequency is 10.8%. Due to the approximate results between simulations and measurements, it demonstrates that the design scheme and principle deduction of primary mirror support system are reasonable, and the FEA modeling is creditable.