The invention relates to an automobile anti-collision alarm system based on pulse laser ranging, which belongs to the technical field of electronics, which is provided with a control circuit, a laser transmitting circuit, a laser receiving amplifier circuit and relevant circuits. A single chip microcomputer STC12C5A60S2 is the core of the control circuit, after laser pulse signals are in spectral processing by a spectroscope with the support of corresponding programs, one channel of the laser pulse signals is reflected by a reflector to be directly received by a PIN receiving circuit, another channel of the pulse laser signals is reflected by an automobile ahead, and then is received by the APD (avalanche photo diode) laser receiving circuit, after receiving time of each of the channels of the laser pulse signals is accurately corrected by a discriminator circuit, the channels of the laser pulse signals are transmitted to the single chip microcomputer master control circuit to be processed, the distance from an automobile with the automobile anti-collision alarm system and the automobile ahead is monitored in real time, and the system can give a sound and light alarm when the automobile is in danger, simultaneously reminds a driver of controlling automobile speed in a voice manner and keeping the distance from the automobile to the automobile ahead. In addition, when necessary, the system outputs brake signals to control the automobile to brake. Besides, the automobile anti-collision alarm system is large in measurement range, high in directivity, interference resistance, precision and practicality, fast in response time and simple in structure, and has high economic benefit and social benefit.