The Chinese characters in Qin of the Warring States era has a special position on the history of Chinese characters, especially, the bamboo scripts unearthed from Qin Tomb at Shuihudi, which can be called the Shuihudi Qin bamboo scripts for short, are the best of all unearthed materials to study the Chinese characters in Qin dynasty for a great deal of popular characters and plentiful fruits of studying. The paper analyses the rationality of the Shuihudi Qin bamboo scripts from two different aspects. Commonly speaking, the Shuihudi Qin bamboo scripts have their own principles, and only 4.95percent ones have no reason. Another way, the pure sign component parts always weaken the rationality, by appearing on the direct component parts stage or appearing on the basal component parts stage.In addition, there are some mistakes on the both stages, resulting in instability of the Shuihudi Qin bamboo scripts system.