The invention discloses a negative pressure regulating device applied to agricultural irrigation. The negative pressure regulating device comprises a U-shaped pipe and a negative pressure regulating pipe, wherein a first communication hole and a second through hole are formed in two side walls of the U-shaped pipe respectively, and the first communication hole is located above the second communication hole; one end of the negative pressure regulating pipe stretches into a left side pipe of the U-shaped pipe through the first communication hole, and the other end of the negative pressure regulating pipe stretches into a right side pipe of the U-shaped pipe through the second communication hole; the left side pipe of the U-shaped pipe is communicated with an external water storage device, the right side pipe of the U-shaped pipe is communicated with atmosphere, and liquid is injected into the U-shaped pipe and the negative pressure regulating pipe; when the water storage device is filled with water to be used for irrigation, the liquid level of liquid injected in the U-shaped pipe is higher than the second communication hole but lower than the first communication hole, the sum of the intensity of pressure of gas in the left side pipe of the U-shaped pipe communicated with the water storage device and the intensity of pressure produced by the height difference of liquid injected into the U-shaped pipe is larger than atmospheric pressure, and the highest height of the liquid level in the left side pipe of the U-shaped pipe is not higher than the first communication hole. By the application of the negative pressure regulating device, the utilization rate of irrigation water can be increased.