Abstract: Uncertainty analysis methods based on WILKS formula is most generally applied for its advantages in reducing the calculation amount. However, the high resolution calculation is required in the nuclear reactor design and safty evaluation , which demand the uncertainty analysis methods with higher efficiency. This paper provides a new method to evaluate the tolerance limit, which is based on the same mathmatical principal of WILKS formula method but with improvements. Compared to WILKS formula method, this new method is capable to decrease the minimum sample size for evaluating the tolerance limit.