In this paper, the surface acoustic wave hydrogen sensor using PdNi thin film as sensing film was studied to realize rapid detection of hydrogen gas. The sensor adopts a twochannel differential oscillator structure, in which the PdNi thin film was deposited by magnetron sputtering method on the surface acoustic wave propagation path of the sensing channel device. The rapid and reversible physical adsorption of hydrogen by PdNi thin films result in the change of surface acoustic wave propagation velocity, and then the frequency signal of the differential oscillator is used to characterize the hydrogen concentration to be measured. The sensing experiments have been carried out to determine the optimum thickness of PdNi for rapid response. The results show that the response amplitude and response time of the sensor are 5 kHz and 5 seconds respectively when the thickness of PdNi is 40 nm.