Positioning with single-plane base array for Ultra-short baseline will lead to increasing of the positioning error when the acoustic source target location is close to the plane of the base array. Multi-element stereo array is introduced to reduce the error by using different array planes combination which can be localized in one stereo array. The stereo array can be divided into several sub-arrays in different directions according to the normal direction of three-element orthogonal array. A positioning calculation algorithm using weighted average of sub-array is proposed, and the affecters for positioning precision of stereo array are analyzed in order to get higher positioning precision. The good positioning results of acoustic source coming from all direction of the stereo array have verified the effectiveness of the proposed five-element stereo array system.