Support technology of large aperture space mirror is one of the key points for space camera development. The influences of stiffness, strength and thermal dimensional stability of the mirror component were considered in the process of support structure design. A support for Φ 980 mm primary mirror in Cassegrain space telescope was designed. The support scheme of six points support on back was proposed in which three points were main and the others were assistant. The problem that surface figure accuracy of large aperture primary mirror meets the demand in the gravity load, but out of errors under the load case of uniform temperature change was solved by adding flexible support. By adopting finite element analysis technique, the static and dynamic as well as thermal characters of primary mirror were analyzed. According to the analysis results, structural parameters of the flexible support were adjusted, and then reduce the influences of gravity, assembly stress and thermal stress on the primary mirror. Analysis and test results indicate that surface figure accuracy of the mirror reaches to PV<λ/10，RMS<λ/50 (λ=632.8 nm), the first natural frequency is 116 Hz, and the maximum stress is 65 MPa in the vibration test, which can meet the requirements for the primary mirror.