Abstract: Under the framework of the free-form spousal property agreement system, the essential difference between the uni-duty and double-duty nature of the gift contract and the spousal property agreement is clarified. The existence of the obligation to pay which is identified in a subjective way is used as a criterion for making a typological distinction between what constitutes a spousal property agreement and a gift contract. In terms of the internal effect, through the way of legal interpretation of the agreement we can reach the conclusion that the direct effect of the change of property rights when the agreement constitutes a spousal property agreement; if the transferee refuses to perform or is unable to continue to perform, the legal right to rescind the contract and the rule of change of circumstances can be applied to remedy the unfairness that may occur. In terms of external effects, regardless of whether the change of property right is registered or not, the principle is to maintain the publicity effect of the property right, taking into account the interests of the transferee and the third party. On this basis, the legitimacy of the spouses' autonomous behaviors still should be examined to prevent them from avoiding debts by means of autonomous behaviors. In the case of the assignor's heirs, the performance of the spousal agreement determines whether its inward effect extends to the heirs. When constituting a gift contract, the agreement is equally applicable to the relevant provisions of the gift contract to produce the corresponding legal effect.