As more and more laser threaten in the war field, the technology of laser warning is becoming an urgent task in the area of optoelectronic countermeasure in order to protect optoelectronic equipment. The basic technical requirement of laser warning and principle of radiation detection are discussed. Based on these theories, two ways to complete laser warning system are presented. According to our practical work, the detailed fulfillment of laser warning system using uncooled infrared focal plane array and experimental result are given.