Abstract: A new method by using the character of the submarine topography will engender gravity gradient is proposed.An example of calculate the gravity gradient of a subulate topography is given,from the example can find that the gravity gradient aroused by the barrier is very big and can easily be observed by the current gradiometer,the result proved the method of this paper is feasible.This study provides a new method for the underwater carrier to avoidance collision,and the method has passive and all-weather characters.