In view of the existing research about document similarity calculation methods based on siamese networks, the entire document is regarded as the input sequence of model that may lead to sparse data. Hierarchical attention mechanism is used to improve the document representation in the siamese network. For the siamese network computing model based on hierarchical attention mechanism may ignore the important sentence in the document when inputting, a two-step document similarity calculation method that introduces the compression of document content is further proposed. The experimental results show that the proposed method is obviously superior to the siamese network computing model based on the Long Short-Term Memory.