Abstract: An experimental apparatus combining ultrasonic wave detection with Time Domain Reflectome-try (TDR) was developed for the first time,and the apparatus can determine gas hydrate saturation as well as acoustic characteristics simultaneously in experimental sediments. The formation and dissociation of gas hydrate can be detected by ultrasonic,TDR and anomalies of temperature and pressure,which gave a con-sistent result in 58 experimental runs. Experimental result reveals that, the apparatus we developed can determine gas hydrate saturation and elastic velocities efficiently. The work is helpful to understand physi-cal properties of gas hydrate-bearing sediments, and it can provide fundamental parameters for the geophysical exploration and resource evaluation of marine gas hydrate.