The bop is mainly composed of main casing, and ram assembly piston, hydraulic cylinder, lead screw, end cap, hand wheel and other spare parts, which are moving in the main casing in opposite direction. When the well needs to be sealed, the hydraulic control and grease injection pressure control system is pressurized to push the piston, thereby leading the two ram bodies to move towards the center of the well bore, and well sealing can be achieved through the associative action of the front rubber sealing element and the top sealing rubber. The ram can be locked on the shut-in position through clockwise rotating the locking hand wheel. What be specially noticed is that before the well is opened, the locking hand wheel must be anticlockwise rotated, the hydraulic control system can be used for pressurizing after the hand wheel is totally receded to the initial position, the piston is hydraulically pushed to led the two rams to rearwards move, and then, the well can be opened. It should be guaranteed to open the full bore to prevent the instruments and the ram from colliding when the well is opened.