This study investigates the role of shaping circuits in lidar systems. Two types of pulse-shaping circuits based on the constant-ratio timing and pulse peak detection methods are designed. Performance experiments on the above mentioned pulse-shaping circuits are carried out in a laboratory and under external conditions to investigate the performance of different pulse-shaping circuits in lidar systems. The circuits based on the constant-ratio timing and pulse peak detection methods show sub-ns time discrimination capabilities. The time discrimination capability of the constant-ratio timing circuit is slightly affected by distance and echo pulse; therefore, the detection accuracy needs to be optimized. This study provides a reference for the optimization of the ranging accuracy of lidar systems.