The fuel tank explosion is one of main aviation safety threats. The paper analyses the kinds of ignition sources which may appear in fuel tank , by researching the ignition prevention requirement of FAA. Also, the paper researches the method of ignition sources prevention and reduction flammability. As FAA recommending one of the most important methods of fuel tank flammability reduction, the paper describes the inerting system. The inerting system configuration and theory have been described with emphasis. And the functions of subsystems of inerting system have been described.