The invention relates to a document similarity detecting method based on seed words. The method includes: Chinese word segmentation and labeling, dictionary calculation, document expression by limited sentence sets, and document comparison. The method has the advantages that few sentences need to be processed during document comparison, and processing speed is increased; sentences with the words high in word frequency-inverse document frequency are selected during representative limited sentence set selecting, so that the selected limited sentence sets are representative in documents, and influence of unrelated or common-sense sentences on document similarity judging is eliminated; two sentences are compared in a word-by-word manner, so that the influence of similar contents and different narration manners is reduced; same words are weighed by inverse document frequency, higher weights are given to the words high in distinguishing performance, and comparison performance is increased.