We compare the detection performance of coherent detectors and single photon detectors, and explain the working principle of single photon detectors under the direct detection system by utilizing binary accumulation. Based on actual lidar parameters and experimental data, the conclusion that the detection performance of coherent detectors is better than that of single photon detectors is clarified. Additionally, the influence of analog-to-digital converter sampling and polarization on coherent detection is analyzed, with relevant requirements for the design of coherent detection ladars provided. We propose a linear mode InGaAs array detector structure based on the laser local oscillator and binary accumulation, which features moderate computational complexity and better detection performance than single photon detectors. On this basis, the parameters of the lunar lidar are basically designed. This lidar can achieve high-precision three-dimensional imaging at a long range and has strong anti-background interference ability.