诉讼时效届满之后的给付,无效法律行为履行之后双方互不追究,不法给付的事实后果,能够产生什么法律效力,在我国现行法中没有定论。本文通过对债的本质属性的界定,在肯定自然债的“债”的属性的同时,对其进行类型化分析,提出“不完全债务”与“纯粹自然之债”的双重类型的自然之债。对自然之债的意义脉络和立法路径进行梳理,并提出解决方法。同时,将与自然之债容易混淆的不法原因给付制度进行论述,提出赋予给付人返还请求权的新观点,并对这一观点的正当性提供依据。 After the expiration of the limitation of lawsuit, the invalidation of the legal act after the fulfillment of each other does not pursue the facts and consequences of illegal payment, what legal effect can be produced, there is no conclusion in the current law of our country. By defining the essential nature of the debt, this article classifies the nature of the debt as affirming the “debt” of the natural debt, and proposes “incomplete debt” and “pure natural debt”. Double type of natural debt. The significance of natural debt context and legislative path to sort out and propose solutions. At the same time, it discusses the payment system of illegitimate reason easily confused with natural debts, puts forward a new view that gives the payer the right of return, and provides the basis for the justification of this view.