Abstract: The large aperture primary mirror(PM) is the key component of space remote sensor. The mirror's stiffness and strength effect on the image quality crucially. In the early days of structural design, FEM analysis and dynamic test were performed on a Ф750 mm primary mirror assembly(PMA) to predict its maximum stress response under random vibration for safety margin. Firstly, the dynamic environment undergone was discussed by the space remote sensor and the equivalent sinusoidal load for random vibration. Then, the FEM model of PMA was built up to simulate the dynamic response using the equivalent loadcriterion. Finally, the dummy primary mirror made of Al alloy was manufactured and dynamic test was performed to acquire the stress response. The analysis and experiment results show that the maximum stress of PMA flexure under random vibrationare is 102.3 MPa、99.5 MPa、104.3 MPa, differ from the analysis result by 10.8%. The analysis accuracy is verified by test results, indicating that the flexure design is reliable to have a safety factor of 2.07, and the PMA can satisfy the design demands.