The primary mirror is the core part of the telescope, and the protection mechanism needs to be designed to maintain its performance and extend the service life of the main mirror film.On this background, according to the structural characteristics and project requirements of a 2.5-meter large aperture optical telescope, a segmented synchronous folding primary mirror protection mechanism is designed.The optimization design of the protective cover plate of composite sandwich material is emphasized, so that the stiffness and strength can meet the relevant requirements while meeting the requirements of lightweight.(Cover plate mass <2.5kg, first-order mode about >20Hz, encountered eight-level wind load and 1kg block impact Tsai-Wu <1). At the same time, through the driving design and control mode test of the folding movement of the mechanism, the multi-fan synchronous driving can be realized in the specified time, and the unidirectional folding movement time is about 52s.This design has a good protection effect on the main mirror and even the entire internal structure of the main mirror tube.This design provides a new idea and validation for the main mirror protection mechanism of large aperture telescopes in China, and has a certain reference significance for the research of other main mirror protection structures.