Abstract: On the basis of the construction of the fault tree of vinyl chloride monomer tank explosion,and according to the statistics of running condition of field equipment and the fuzzy information provided by expert experience,a reliability analysis on vinyl chloride monomer tank was firstly made by using fuzzy fault tree theory,introducing L-R fuzzy number and applying a sharp-state-typed membership function.Then the fuzzy probability distribution of the explosion was gained,and the structural analysis of importance wag conducted by using structural important coefficient approximation method.Finally,the major factors affecting vinyl chloride monomer tank explosion were decided by rating the bottom events of the fault tree with the importance-weighted structural analysis.