The invention discloses a coal adsorption/desorption methane experiment device and method under an ultrasonic action and belongs to the field of coal adsorption/desorption methane experiments. The device is composed of a gas supply system, an adsorption/desorption system, an ultrasonic system and a temperature control system, wherein the adsorption/desorption system comprises an adsorption/desorption cylinder, a distribution cylinder, a high-precision gas digital sensor, a vacuum pump, a computer host, a display, a draining bottle and a measuring cylinder; the ultrasonic system comprises an ultrasonic generator, an ultrasonic transducer and a thermostatic water bath; the temperature control system comprises a heating pipe and a temperature sensor; the adsorption/desorption cylinder and thedistribution cylinder are both immersed in the thermostatic water bath; the ultrasonic transducer and the temperature sensor are arranged outside the thermostatic water bath; and the heating pipe isarranged at the bottom inside the thermostatic water bath. The device and the method, disclosed by the invention, can be applied to laboratory investigation of isothermal coal-to-methane adsorption/desorption rules by ultrasonic waves of different power and different frequencies at different temperatures.