Chinese and foreign scholars have consensus that Voluntary principle is a fundamental principle of mediation in the civil procedure. Although the value of the voluntary principle is cherished by all persons, but the domestic theoretical studies ignore one very important question: As one state changed from natural state to civil society, the original natural rights people enjoyed will be limited, the voluntary principle in mediation is institutionalized, it will be subject to some restrictions too. Ignoring this problem will lead to some mistakes, and thus wrongly critique some legislative and judicial phenomenon. With the help of comparative method, contrasting the state of voluntary principle before it being institutionalized and the state of voluntary principle after it being institutionalized will help avoid such mistakes.