The development and actuality of laser passive reconnaissance warning device are sketched. The composition, operation principle and features of the system are introduced. The design of laser probe and data processor of the laser warning device are emphasized. InGaAs Pin photodiode is adopted in the optoelectronic detector of the probe. The data processor comprises threshold circuit, discrimination circuit of pulse bandwidth and twoecho signal restraining circuit. Firstly, the laser signal is digitized under the condition that the signal is affirmed. Then the incident orientation of laser is calculated. Finally, the laser ranging signal and guiding signal are distinguished by threat style and grade curcuit on the basis of threat database. The system has the advantages of high sensitivity, rapid response and wide dynamic range, and it can be linked up with smoke discharging equipment. The system and other defense equipments can be connected by preparatory communication interface.