To solve the uncertainty reliability problem of a high reliability structure, a separable Monte Carlo (SMC) method based on crude Monte Carlo (CMC) method and Condition expectation (CE) method is proposed. The method uses different sample size of response and capacity, and replaces the distribution function of CE with empirical distribution function of sample of SMC. Practical example of reliability shows that SMC method not only solves the calculation cost, but also improves the calculation precision, it can be applied to uncertainty reliability problem of structures.