Abstract: On the basis of briefly introducing the current air flow measurement system of mine main ventilator in China, in view of the existing problems in main ventilator on-line monitoring system, such as uneasy to calibrating air parameters online, easily blocked the pressure sampling tube, can not distinguish the positive and negative direction, in addition, can not guarantee the accuracy of long-term operation, multi-channel ultrasonic time difference method is used to design main ventilator air volume monitoring system based on ultrasonic flow measurement principle and the structure, working principle and function of the system is introduced in detail.