The combination of passive infrared and active microwave is a kind of dual detector. Based on the working mechanism of dual detector, the calculation and detail design of various kinds of window materials are carried out. The low loss of active microwave and passive far infrared signal is realized. The problem of the application of dual detector in the environment of explosion-proof requirements is solved by the explosion-proof box designed. It is of great significance to enhance the level of anti-intrusion monitoring technology in dangerous environment such as flammable and explosive.