Tsun Tze was a rear guard figure in Confucianism and the best thinker who discounted Pre-Qin Confucian thoughts of law systematically in Warring Period. His relative discourses on Ritual and Law have greatly influenced development of Chinese System of Law afterwards. However, what we regret is that Tsun Tze did not receive enough honors before middle Qing Dynasty, and his study on Thought of Law was neglected associatively. The Ritual that Tsun Tze perceived is actually Today's Law. In other words, it is the objective norms possessing a kind of objective norms with substantive value and the legitimate source that nation exerts power. In this paper, the author began with discerning relation between Ritual and Law, and then further indicated Ritual's serving as a kind of superior norms that develop four main functions in Tsun Tze's System of Law as follows. 1. Ritual is the foundation of constructing the objective systems, and it has substantive value itself to produce all written norms. 2. Ritual is the principle appropriate to be used to deduct laws. By the truth contained in Ritual, Law's weakness and insufficiency is therefore made up. 3. Ritual is the standard to divide rights and duties, and it is the greatest common divisor identified by social value. Consequently, we should distribute the rights and obligations to people in different social groups by Ritual to achieve positive equality through ”differential treatment”. 4. Ritual is the root foundation for the society to distribute justice, so that social resources can be brought to a full play. Finally, this paper also illustrated the difficulties appearing in Tsun Tze's theories of Ritual and Law. Since he denied ”Heaven of Morality” and ”Heaven of Personality” externally, while holding ”Theory of Evil Nature in Mankind” internally, the legitimacy of Ritual cannot be consolidated then, leading to an enormous theoretical dilemma in Tsun Tze's System of Law.