Based on the statistics of running condition of field equipment and the fuzzy information provided by experts, the fault tree of fire accident in cotton plant is constructed. A reliability analysis on fire accident is made by using sharp-state-typed membership function of the fuzzy fault tree theory, then the fuzzy probability distribution of the explosion is gained.The structural importance of each basic event is also analyzed, and the most influencing factors are determined. It provides a new way for safety analysis of the system and prevention of fire accidents.