The angle between signal light and local light is an important factor affecting the heterodyne detection. Even a small angle will lead the intermediate frequency signal to be weak. It is pointed out that the amplitude of the intermediate frequency signal can be regarded as the Fourier transform of the distribution function of quantum efficiency of detector. Based on that, a method using array detector in which the gain of unit is adjustable is proposed. One can form an effective quantum efficiency function matching the spatial mismatch angle by adjusting the gain magnification coefficient, which can enhance the intermediate frequency signal intensity. According to the method, high-speed scanning detection can be realized by a programmable controller.