This paper is a study of the theory of human nature of the Pre-Chin legalist school with “Kuan Tzu”, the “Book of Lord Shang” and “Han Fei Tzu” and main reference. It is divided into the following sections: (1)prologue, (2)underatanding of human nature as the necessary condition for governing the world, (3)analysis of human nature in “Kuan Tzu”, (4)analysis of human nature in the “Book of Lord Shang”, (5)analysis of human nature in “Han Fei Tzu”, and (6)examination and appraisal of the theory of human nature of the Pre-Chin legalist school. The present author’s analysis shows that the Pre-Chin legalist philosophers refrained from commenting on the question whether human nature is essentially good or evil. Their main concern is how a ruler could adequately govern the nation. In order to govern the nation, it is necessary to carry out empirical studies of human nature without making value judgments. The three main texts mentioned above all agree that emotions and desires are the basic elements of human nature, but they differ in details. The theories of human nature in “Kuan Tzu” and in “Han Fei Tzu” are, because of their Taoist intent and insight, especially profound and complicated.