Based on the risk of steam injection boiler, and contingency and uncertainty of each basic events , the triangular fuzzy number was used to show the probability of events, then get the top event probability. Combined with the fault tree analysis and fuzzy mathematics, through the fuzzy operation, the interval value of failure probability of hazards of steam injection boiler was obtained, and the fuzzy importance degree, sequence and main factors were determined. Drawing a fault tree based on various risk factors, using the method of minimal cut sets and Boolean algebra method, the boiler burst pathway tubes were showed, and fuzzy probability causing the accident was arrived. The causes of the accidents were analyzed, and protective measures of the steam injection boiler were proposed.