The output signal of photon counting lidar has serious distortion phenomenon under the high-flux condition,which affects the extraction of target information.Therefore,to investigate the change rule of signal distortion,this paper establishes the steady-state forward recursion model for signal calculation of photon counting lidar under the condition of multi-trigger.The model has many advantages,such as high precision,fast speed and accurate reflection of physical process.The influence of the echo signal distortion is explored by changing the signal amplitude N,the pulse width PW,the background noise Nb and dead time Td of the model.Results show that when the dead-pulse-ratio Rdp≤2,the signal distortion is related to N,PW and Td,when Rdp>2,the signal distortion is only related to N.At the same time, our simulations show that when the detection loss rate α≤5%,the influence of signal distortion can be ignored, which can be used to distinguish high-flux signal distortion (α>5%) and the fidelity of the low-flux signal (α≤5%).According to the calculation,changing the length of the dead time converts the high-flux to the low-flux under some specific conditions.Compared with the traditional "5%" criterion based on photon count rate,the above conclusion provides a more accurate boundary between the high-and low-flux and signal distortion.