Abstract: In order to protect the primary mirror of a meter-class telescope, the petal-type cover was designed. The main structure form of lager aperture telescope which have completed at home and aboard were introduced briefly. On the basis of offset slider-crank mechanism which was evolved from four-bar linkage mechanism, a four bar structure which did not need brace existing was proposed. In addition, the kinematic model was created and the force analysis was carried out. The driving torque of motor, displacement of slider and operation time of cover were calculated. Practical application shows that the cover is reliable and effective to prevent the dust and dropped objects from polluting or damaging the primary mirror. The time to open or close the cover is about 62.5 s. The life of no fault is more than one year using in Changchun area. The operation number of no maintenance are more than 500. So the design satisfies system requirement and provides reference for the coming researchers.