Aimed at the problems that the description of importance analysis is complex, abstract conception is uncertain, and these are unfavorable ordering for fuzzy fault tree analysis, a new importance analysis method based on structure vector is proposed. First of all, the trapezoid fuzzy number is abstracted as uniformity trapezoid and its change is abstracted as the shifty vector of the trapezoid center. And then, the horizontal mapping of shifty vector is used to define the variation of error rate and vary rate of error rate. Meanwhile, the vertical mapping of shifty vector is used to define the irresolute degree of trapezoid fuzzy number. At last, the fault of cooling system of a certain radar is treated as the top event, and the method proposed is proved by importance analysis.