Aiming at the product whose performance degradation process obeys to Wiener process, a residual lifetime prediction method is proposed by combining online measured performance degradation data of a product with normal degradation data of like products. Assume that distribution parameters obey to union conjugate prior normal-inverse gamma distribution, a Bayesian estimation model of distribution parameters is built up under individual online measured degradation data. Posterior estimation formula of hyper parameter is obtained. The complete likelihood function of degradation test data is built up. Prior estimation model of hyper parameter is established based on Expectation Maximization (EM) method. Accuracy of the method is verified by an example.