By means of fuzzy fault tree analysis method

a systemic analysis of the relevant factors which caused the output instability of electro-hydraulic actuator is carried out

and its fault tree is also established. It processes the experts group estimation on the fault without statistical information by using expert graded method. The way of changing into fuzzy math is expatiated

and the happening probability of all the base events are presented with triangular fuzzy number. The fuzzy fault tree algorithm is used to calculate the confidence interval of top event and each subsystem

and the fuzzy signifi cance of basic events is obtained. Then the way for the system improvement is pointed

which provides large complex electro-hydraulic actuator references for reliability analysis.