The invention discloses a U-shaped pressure meter and a pressure measurement method thereof. In the U-shaped pressure meter, the bottom of the U-shaped pressure meter is communicated with a liquid feed tank through a liquid feed pipe; the right pipe section of a U-shaped pipe extends in the horizontal direction into an overpressure overflow protection tank; the left pipe section of the U-shaped pipe is communicated with a high pressure measurement mouth pipe and a horizontal connection pipe, and a three-way valve is arranged at the joint of the left pipe section of the U-shaped pipe, the highpressure measurement mouth pipe and the horizontal connection pipe; the external end of the horizontal connection pipe is communicated with a horizontal escape pipe and a piston air measurement cylinder, and another three-way valve is arranged at the joint of the external end of the horizontal connection pipe, the horizontal escape pipe and the piston air measurement cylinder; and the volume scale is marked on the left pipe section of the U-shaped pipe. The pressure measurement method comprises the following steps of: disconnecting the high pressure measurement mouth pipe and the U-shaped pipe by the three-way valve; connecting high-pressure gas in the U-shaped pipe and the piston air measurement cylinder; and measuring the volume of high-pressure gas in the U-shaped pipe under normal pressure by using the piston air measurement cylinder and calculating to obtain pressure of the high-pressure gas. The invention has the characteristics that the measurement accuracy does not change along with the rise of pressure, and when the measurement pressure is higher, relative error is smaller.