Abstract: This paper has analyzed principles of passive infrared and microwave detection technology. A design method of explosion-proof infrared microwave detector based on flame-proof and intrinsic safety is proposed. In this method, DT8035 composite intelligent detector designed by Honeywell is transformed into intrinsic safe circuit. And the corresponding circuits are designed, including intrinsic safe electric power and signal isolation circuit. The detector can used in explosive environment, such as underground pipe gallery.