In order to solve the parameter estimation problem of three parameter Weibull distribution,the gray estimation method was presented to estimate the parameter of three parameter Weibull distribution.Based on the random censored data of hydraulic oil tank pressure relief valve in the using phases,the parameters of three parameter Weibull distribution were estimated based on GM(1,1).The results show that using grey model GM(1,1) can estimate the three parameters of the three-parameter Weibull distribution,avoiding the iterative process;the proposed method is fast solving speed,few samples required,more accurate,easy programming and so on;it is also verified that the three-parameter Weibull model is more accurate than the two-parameter Weibull model,which can provide a more accurate method of reliability analysis for military equipment in the using phases.