The invention belongs to the field of dilute acid tank auxiliary devices, and relates to a dilute acid tank breather valve which comprises a communication pipe, a first shell and a second shell. The first shell is provided with an air inlet, a first accommodating pipe and a first valve body, and the second shell is provided with an accommodating hole, a second accommodating pipe, a supporting plate, a second valve body and a supporting sleeve. The lower portion of the second valve body is arranged in the second accommodating pipe, a liquid outlet pipe is arranged in the accommodating hole, a first fixed flange plate is arranged on the upper portion of the liquid outlet pipe, and a sawtooth groove is formed in the bottom of the liquid outlet pipe. A liquid inlet pipe is arranged on the lower portion of the middle of the communication pipe, and a second fixed flange plate is arranged on the lower portion of the liquid inlet pipe. The first shell and the second shell are arranged at the two ends of the communication pipe correspondingly, the valve bodies are arranged in the corresponding shells, the problem of positive pressure and negative pressure can be effectively solved, and the dilute acid tank breather valve is quite simple in structural design, quite low in cost and very suitable for acid tanks.