Abstract: There is no standard for intrinsically safe electrical system of coal mine underground internally, and technique rules for I type intrinsically safe system are uncompleted in the new IEC 60079-25. The paper gave the concept of intrinsically safe electrical system and analyzed particularity of explosive environment of coal mine underground. For intrinsically safe electrical system whose whole or some parts are needed to reach protection level of I type EPL Ma or EPL Mb and explosion-proof type is intrinsic safety type “i” when used in explosive environment of coal mine underground, it expounded keys of system structure design and explosion-proof parameter evaluation and proposed some practicable methods. It also proposed fault analysis methods for system equipments and cable. Finally, it analyzed current status and development trend of intrinsic safety technology internally and overseas.