According to the error characteristics of the echo of diffuse reflection laser ranging, a real-time echo-photon detection method is proposed based on the motion compensation and robust estimation. By using motion compensation, one can increase the number of accumulation photons to provide a reliable initial value. Based on this, by adoption of robust estimation scheme to removing gross errors of observation data, one can realize the real-time online detection of echo-photon effectively. Experiment results show that, under the condition of low signal-to-noise ratio, the method can not only suppress the impact of noises, but also effectively solve the real-time signal detection problem in diffuse reflection laser ranging.