Abstract: When the Qing dynasty was compiling Siku Quanshu, almost all the included books had been revised, which contained two cases: changing the names of ethnic languages and making corrections and deletions of the suspected taboo words. In fact, the specific situations were complex. In the former aspect, during the compilation of Siku Quanshu, except certain books, such as the history of Liao, Jin, Yuan etc., had been completely changed the names of ethnic languages, as well as some books modified as appropriate, the rest were practically unchanged. As for the later aspect, those corrections and deletions were rigid for the books written in the late Ming and early Qing periods, while loose for the books before the late Ming dynasty. However, until the phase of proofreading Siku Quanshu in 1787, the measure of revision became extremely rigorous, so that all the books concerning the periods of Liao, Jin, and Yuan had been completely modified and bowdlerized in both aspects. In this study, the version of Sanchao Beimeng Huibian used for proofreading Siku Quanshu, collected by Shanghai Library, has significant documentary values.