An online-increment evolution topic model based automatic software classifying method includes acquiring relevant software texts, grouping and preprocessing by a preset time slice; generating a probability model of an online evolution topic model, computing the number of the optimum topics according to project description texts grouped according to the time slice, and incrementally computing topic word distribution and topic text distribution of the project description texts within the current time slice; acquiring a text d of an unknown classifying topic, computing topic word distribution of n topics subordinative to the text d according to the topic word distribution and the topic text distribution, classifying the text d into corresponding topics, and automatically adding semantic tags to the topics based on the word list and word inquiry method, and finally completing classification of software projects. By the online-increment evolution topic model based automatic software classifying method, new topics appearing in open source communities can be found in time, software projects can be automatically classified, a software developer can search out required open source software projects according to software topics conveniently, and accordingly, software development efficiency is improved, and quality and assurance of the open source communities are improved.