This article aimed at the current problem of hydrogen gas detection technology put forward a detection of ultrasonic phase difference. This detection design according to the different sound speed from hydrogen and other gas，utilize dual-channel design，skillfully converted ultrasound velocity into phase difference，phase difference change measured to reflect changes in gas concentration，improve the measurement accuracy，and usingdigital temperature sensor recompense temperature， expanded operating temperature range of the sensor. Experimental results show that the measurement method to achieve a hydrogen fast，high-precision，low-power， low-cost testing，has a high theoretical and practical value.