Abstract: The spatial matrix filter is designed and used to solve the problem that the weak target is influenced by the strong nearby platform interference of towed line array sonar. The matched field processing technique and the direction of arrival estimation technique were combined together by using of the sea sound propagation characteristics. The spatial matrix filter with platform noise zero response was designed by the copy vector of the nearby platform noise and the bearing vector of distant plan wave transferred to the array together. The optimal solution of the spatial matrix filter design problem was deduced directly and was simplified by the generalized singular value decomposition. The total response of plan wave bearing vector and the total response of platform noise copy vector were given. The phenomena that strong interferences exist in the bearing course and the bland areas exist after using the spatial matrix filtering technique were explained by the relativities between the platform copy vector and the plan wave bearing vector. It can be found by simulations that less bland area and higher detect ability can be achieved with spatial matrix filter processing.