Method for detecting methane concentration by ultrasonic waves

The invention discloses a method for detecting methane concentration by ultrasonic waves. The method includes that gas to be detected is freely dispersed into two static speed pipes communicated with a measuring pipe after flowing through the measuring pipe, ultrasonic transducers used for measuring propagation velocity of ultrasonic waves in the static speed pipes are disposed on the two static speed pipes respectively and transmit and receive the ultrasonic waves so as to acquire practical propagation time of the ultrasonic waves during corresponding sonic path measuring, and the corresponding measured sonic path divides the practical propagation time of the ultrasonic waves in the corresponding static speed pipes to obtain propagation speed Cf1 and Cf2 of the ultrasonic waves in the two static speed pipes; the propagation speeds Cf1 and Cf2 of the ultrasonic waves are introduced into a calculating formula to obtain propagation speed of the ultrasonic waves in the gas to be detected, and then the methane co