Pulsed laser ranging system is widely used in laser radar, laser guidance and other fields due to its advantages of high precision, strong anti-interference ability, etc. However, the commonly used timing discrimination method has errors and restricts the improvement of dynamic ranging accuracy, which was mainly caused by the attenuation and widening of the echo pulse. A new method of timing discrimination was presented in view of this problem, which was based on the dual-channel timing discrimination method. The dual-channel timing discrimination method was composed of constant threshold timing discrimination method and peak timing discrimination method. Through the dual-channel timing discrimination method, accurate echo timing discrimination can be achieved without being affected by attenuation and broadening. By introducing the theoretical equations of the laser emission pulse, the time domain distribution model of the echo waveform was established. The experimental results show that the short ranging error can be controlled within ±3 cm by adopting the dual-channel timing discrimination method, and the accuracy can be further improved by multiple measurements, which solves the bottleneck problem that the timing discrimination error restricts the dynamic ranging accuracy.