Abstract: Trust relationship between users in a social network can provide ground to user to judge whether the information is trustworthy．Existing method of trust computes usually computes trust by searching the paths from source node to target node,and/or adding some external limitations,such as the length of path,the minimum trust values and so on．Few of them considers the similarity between nodes．This paper combined the trust propagation model with the similarity between nodes,and computed the distribution of the similarities between nodes by Bayesian probability formula．We also analyzed the influence of decay coefficient on the result and found the similarity between trust users is much higher than un-trust users in order to demonstrate the Bayesian probability formula can improve the method by data statistical analysis．At last,a trust propagation model based on probability was presented．After experiment on Epinion datasets,the validity of our method is proved by the result.

Key words: Trust,Social network,Web of trust,Trust prediction