We proposed a flexible anti-plagiarism system model based on user-defined plagiarism standards. We also proposed PlagLazy and format-legacy phenomena that plagiarist will remain format-legacy such as soft-enter symbol in his DOC document after plagiarizing material from web and corresponding optimized algorithm which improves the speed of comparison. Our model is suitable for the anti-plagiarism and monitoring of large document collections, and it can also be used in digital library, E-learning and other fields.