The invention provides a question and answer community expert recommendation method for performing interest modeling by use of tag fusion across platforms. According to the method, cross-platform common users are utilized to construct word vectors of tags by combining an LDA topic model and word2vec, a tag semantic similarity matrix is constructed for text data of different platforms, a fusion feature space is generated, and a fusion space model of the users is obtained. Compared with a single-network user model, the cross-platform user model can cover different features of the users more comprehensively, and the user features are described more clearly. Meanwhile, answer abilities of the users and cross-platform community influences of the users are comprehensively considered, a PageRank algorithm based on a fusion network is used to perform authority evaluation on the users, and then community feedback is considered to perform ability evaluation on the users. Through experiment comparison with a reference interest model, the single-network user model, a collaborative filtering recommendation model and other algorithms, it is shown that the algorithm has a better recommendation effect.