For the high dynamic range of echo signals in some lidar systems, it can be challenging to achieve high performance acquisition of the strong and weak signals simultaneously. A hardware and software joint acquisition method is proposed, which uses a high-speed digitizer to acquire the full waveform and then deals with the algorithm software. For the software photon counting algorithm, a dynamic voltage threshold selection method is also proposed to improve the counting accuracy. The simulation model of devices in the full-link of photoelectric detection and acquisition is established to compare and verify the feasibility of the methods. Based on a set of typical parameters of preferred devices, the simulation compared the acquisition errors of the full waveform acquisition method with the existing methods, verifying the effectiveness and technical advantages of the full waveform acquisition method and the dynamic threshold selection algorithm. This research provides a novel idea for the detection of weak optical signals with high dynamic range by leveraging a synergistic combination of hardware and software techniques.