Fire detecting system is a important part of the fire extinguishing and the explosion suppression equipments which can be used to protect the safety of people when the fire broke out in special vehicles. The systems based on temperature sensor and non-imaging photo-detector which are usually used now have some problems because the space structure of engine bay is complex. For example, the system based on temperature sensor often fails to find the fire because the distance between senor and fire is too large, and it is impossible for full coverage of the Engine Bay space. Also, the fire detecting system based on linear or spot heat detector often fail to detect the fire in time used for engine bay overheat protection. And the system based on non-imaging photo-detector often fails to alarm the fire because the sensitivity is too high. So the fire and explosion seriously threaten the safety of armored vehicles and the people in them. To solve the problem, a detecting system based on infrared imaging technology is designed. A infrared-imaging detector is employed. A display and control unit is used to monitor the engine bay temperature. The temperature threshold can be preset for early warning of high temperature and fire alarm. Engine bay overheat protection system based on infrared imaging technology is tested by normal blaze experimental platform which is made up of a normal brazier and a exhaust equipment. Experiment results show that the system can generate alarm signals when the temperature in engine bay space is higher than the temperature threshold. And fire response time based on this infrared imaging system is less than 5 s, which can meet the requirement of relevant National Military Standards of China. As a result, the system can be used for fire early warning, and can meet the requirements for engine bay unreported fire. This system can be used to protect armored vehicles and safety of people in them.