The philosophers in the ancient Qi had controversial views on human natures. Famous theories like Mencius's ”good essence”, Gaozi's ”null essence”, and Hsun-tzu's ”bad essence” were the most representative. Gaozi's view was neutral, while Mencius' and Hsun-tzu' views seemed to be contrast, but they were not contrary, in fact.This study tries to elaborate on the theory advocated by Hsun-tzu. Via the analysis of bad essence, the author explained the meanings of human nature, and Hsun-tzu's criteria of judging good or bad human natures. The author also stated the way Hsun-tzu educated people to turn the bad essence into good behaviors. The significance and the values of good behavior acquisition are highlighted in this study.