MTi motion sensor measured the heave motion of the supporting ship. The motion of the MTi was controlled by a servo-motor system which determined the period and range of heave motion. The integral of output of MTi acceleration was dealt with a digital high-pass filter which eliminate the low-frequency noises. So the heave speed of the supporting ship was obtained. The simulation model was set up. And the semi-physical simulation test was done with the input of velocity that measured by MTi. Semi-physical simulation test shows that active heave compensation unit of underwater vehicle is a good way to improve the security of underwater vehicle.