The detector in a highly accurate and high-definition scanning 3D imaging lidar system requires high frequency bandwidth and sufficient photosensitive area. To solve the problem of small photosensitive area of an existing indium gallium arsenide detector with a certain frequency bandwidth, this study proposes a method for increasing the receiving field of view (FOV) and enlarging the effective photosensitive aperture of such detector through hexagonal prism beam splitting. The principle and construction of hexagonal prism beam splitting is also discussed in this research. Accordingly, a receiving optical system with two hexagonal prisms is provided and the splitting beam effect of the simulation experiment is analyzed. Using this novel method, the receiving optical system's FOV can be improved effectively up to ±5°, and the effective photosensitive aperture of the detector is increased from 0.5 mm to 1.5 mm.