In order to solve the situation that the 2.4-meter telescope cannot switch Nasmyth focus and Cassgrain focus intelligently, a switching system was designed to switch focuses rapidly to improve the observation ability. Firstly, a M3 switching system model was built, the composition and implementation of the system were discussed in detail. Then precision analysis and finite element analysis were performed to optimize design. Finally, the calibration and test were carried out through experiment. Finite element analysis shows that under the action of gravity, the mirror surface shape RMS<λ/60 (λ=632.8 nm). The first-order modal of system reaches 34.71 Hz, the system has good stiffness. Experimental measurement shows that azimuth structure and altitude structure repetition precision are superior to 0.5″, translation stage repetition precision is 1 μm. The switching system meets the performance requirements and has been installed in the telescope, which has been used for observation. It also provides a reference for the design of other telescopes.