Logical analysis is an important method of scientific research, which should be applied consciously in studying philosophy and history. Mr. Gu Jiegang(1893-1980) had a solid foundation in the studies of Chinese ancient civilization and wrote prolifically on the subject, but he didn't know how to apply this method to his research. Therefore, although the “Doubting Ancient History” Movement advocated by him had made outstanding achievements, some of his important textual research can't stand logical analysis, like castles in the sand. For example, in “the Study of the Evolution of Ancient Scholars,” Mr. Gu applied simple enumeration method, but used it as the universal for inductive judgment; in the study of the Xia Dynasty, the Analects of Confucius could be used as a supporting point, but Mr.Gu abandoned it. He followed Kang Youwei (1858-1927) in his “study of the Old Texts and the New Texts of the Confucius classics of the Han Dynasty,” arguing against logic, taking a part as the whole and reversing the time sequence. Both the grounds and conclusion of the arguments are wrong. Mr. Gu himself admitted that he didn't know logic, nor did he understand deductive reasoning and major premises as the basis of argument. Therefore the truth and falsehood of his arguments must be strictly analyzed and tested.