Using polyaniline as a sensitive material, a highly sensitive and fast-response surface acoustic wave (SAW) ammonia gas sensor device was experimentally prepared, and a sensing system was constructed by combining with a phase-detecting sensing circuit, The mass load and the acoustic-electric coupling effect generated by the selective adsorption of polyaniline to ammonia cause the change of the sound propagation velocity, and then the voltage signal output by the phase detector is used to characterize the volume concentration of ammonia to be measured, The experimental results show that the sensor exhibits high sensitivity (0, 11 mV/10-6 mV), low detection limit (0, 5×10-6) and fast response time (T90<20 s) at room temperature,