The invention is suitable for the field of social network information recommendation and provides a probability matrix decomposition-based community trust recommendation method and system. The method comprises the steps of obtaining behavior data of users, and obtaining a community set; building a community data model according to user information, a user relationship, project information required to be recommended and the community set, and obtaining a trust relationship among the users; building a probability matrix decomposition model according to the trust relationship, solving the model, and performing calculation to obtain recommendation information; and recommending required project information in the recommendation information to corresponding users according to a predetermined recommendation rule. According to embodiments of the method and the system, a community relationship of the users is introduced in the trust relationship, and the users in the same community are distinguished from the users in different communities, so that the trust relationship can reflect a real relationship among the users more accurately, the situation that a one-sided interactive relationship is regarded as the trust relationship is avoided, and the accuracy of a trust-based recommendation algorithm is greatly improved.