The Io plasma torus is the most densest and most widely studied region of Jupiter's magnetosphere. To meet observe the Io plasma torus observation， a Lyot Coronagraph was installed in the planet's atmosphere spectrum telescope to meet the needs of imaging observation of Io plasma torus capture the emissive spectrum. The parameters of the instrument were determined according to the radiation characteristics of the Jupiter and the parameters of PAST. Then， the initial structure was optimized. The imaging performance of the system was analyzed， and the MTF value at 37 lp/mm is above 0.6 that meet the design specification. Considering the character of stray light in system， a structure system for suppressing stray light was built considering the characteristics of stray light. The level of stray light in the system was measured in a class 1 000 cleanroom. The experimental results show that the main sources of stray light can be suppressed entirely， and the stray light suppression level of the system is equal to 10^-5 at 2.5R_j， which satisfies the system requirements for observing Io plasma torus.