The invention discloses a valve easy to control on-off thereof. A valve rod is connected with a valve rod sliding rack. A square valve plate is connected with a valve cover via a valve plate rotating shaft. Guided by the valve rod sliding rack, the square valve plate is upwardly opened around the valve plate rotating shaft and is locked below a valve cover. A housing of a round square valve body is provided with a valve input hole for connecting the valve to a pressure vessel. The valve input hole is connected with a lower pressure chamber of a trigger device via a piston. A valve seat is shifted between a closing position of closing the piston and an opening position of closing the piston. The valve also comprises a pressure regulator in pressure connection with the valve input hole and the lower pressure chamber. The valve plate can be upwardly opened with 90 degrees, fluid resistance is little, the fluid can flow rapidly and smoothly, the processing flow is short, the technology is simple, the two pressure chambers are separated by controlling the piston, and the control is sensitive.