Provided is a high-precision Gm-APD laser radar system based on multi-door full-waveform response and a range finding method thereof, belonging to the technical field laser detection, and solving the problem that the conventional Gm-APD needs a certain time to suppress the avalanche current after the response, so that the range finding precision of a Gm-APD laser radar is seriously influenced. The laser signal emitted by a laser is incident to the incident end of an optical emission system and the detection surface of a PIN detector after being split by a splitter; the optical emission system emits laser pulse signals; the detection signal output end of the PIN detector is connected with one laser detection signal input end of a door control processing module; the other laser detection signal input end of the door control processing module is connected with the detection signal output end of a Gm-APD detector, and the laser pulse signal received by the optical emission system is filtered by an optical filter and then is incident to the detection surface of the Gm-APD detector. The high-precision Gm-APD laser radar system and the range finding method are applicable to long-distance high-precision range finding.