a medium which enters from the inlet 400 flowing out of the outlet 500 one end of the valve rod 310 is in threaded connection with the baffle plate 330 so the pressure regulator is convenient to be detached when the piston device is away from the valve port 600 the fluid medium flows via the third area a from the inlet 400 flows out from the outlet 500 and simultaneously enters the first area c and the second area b of the piston device and through buffering of the first area c and the second area b pressures of the upper and lower parts of the piston device tend to be consistent and the unbalanced pressure of the upper and lower parts of the piston device is reduced the pressure of the fluid medium flowing out the outlet 500 tends to be stable when the height of the first area c or the distance between the baffle plate and the upper end part of the piston body comes up to a certain value the pressure in the whole pressure regulator tends to be stable the supplying pressure of the medium at the downstream outlet 500 tends to be stable the embodiment of the pressure.