The invention provides a knife of a sandwich structure. The knife comprises two fixed knife bodies and a movable knife body sandwiched between the two fixed knife bodies. A row of comb teeth are arranged at the front end edge of each fixed knife body, and the inner surface, making contact with the movable knife body, of each comb tooth and the side edge of the comb tooth form a sharp corner. A row of knife teeth with knife edges are arranged at the front end edge of the movable knife body. The front end edges of the two fixed knife bodies are overlapped, and the front end edge of the movable knife body is sandwiched between the front end edges of the two fixed knife bodies and is not exposed out of the front end edges of the fixed knife bodies. The movable knife body can be driven to make the front end edge of the movable knife body move horizontally left and right relative to the front end edges of the two fixed knife bodies to achieve shearing. The knife can improve safety and shearing efficiency.