Based on the condition of constant distribution and const logarithmic standard deviation for Lognormal distribution, the Bayes method is used to analyse the accelerated factor of accelerated life test. Firstly, according to the complete life test data and the theory of distribution for function of the random variable, the prior distribution of accelerated factor is presented. Then, combined with a small amount of field type Ⅱ test data, the Bayes formula is used to calculate the accelerate factor. An example is given to illustrate this method.