Abstract: Commonly in the biomass briquetting machine, hydraulic cylinder directly impulses the covering for lock and unlock in the covering mechanism for closing and unclosing. But the unlock angle was finite in this kind of scheme. The angle might impact material feeding, and hydraulic cylinder was too big, so the structure was incompactly. Against those shortcomings, a new mechanism was designed to actualize the function. The new scheme adopted crank and rocker mechanism for lock and unlock the covering. This mechanism was powered by hydraulic cylinder. The covering would be more stable when the dead point appeared. The crank and rocker mechanism was calculated with auxiliary circle, and the model for simulation was established. The requirement of mechanism motion can be realized by simulation.