折价补偿指的是以金钱的形式使当事人间的财产关系恢复到民事法律行为实施前的状态，是《民法典》第157条所确立的法律行为无效的法律后果之一。买卖合同作为典型的财产法律行为、双务合同，在折价补偿的问题上具有一般性和复杂性，这些问题中，折价补偿的性质、构成要件、抗辩事由、金额计算各有值得深入研究之处。《民法典》第157条有关折价补偿的规定属于不当得利返还请求权体系下的特别规定，对折价补偿具体规则的解释应在不当得利的制度框架内进行。在买卖合同中，折价补偿请求权主要发生在标的物毁损灭失、转售给第三人的场合。折价补偿的主体为买卖合同当事人，义务人一般是买受人。买卖合同标的物毁损灭失后，买受人取得的保险金、赔偿金、补偿金应当属于不当得利制度下原物返还的范畴，不应按照折价补偿标准计算；买受人转售所得的对价则属于折价补偿的范畴，应按照折价补偿金额的计算标准予以计算。关于折价补偿抗辩事由，主要存在以下争议：折价补偿义务是否受无效规范目的影响，折价补偿义务人能否通过所获利益不存在、标的物毁损灭失可归责于相对人或意外风险相关事由进行抗辩。本文认为，无效规范目的对折价补偿义务有着有限的影响，双方违法背俗或折价补偿义务人为未成年人情形下，当事人的折价补偿义务存在排除的可能；但欺诈、胁迫等可撤销情形下，相关规范的目的不能作为抗辩事由。由于双务合同的特殊性，标的物毁损灭失或转售后，善意买受人所得利益不存在的，不能援引《民法典》第986条免除针对标的物本身价值的折价补偿义务。此外，折价补偿义务的范围不受当事人对标的物毁损灭失的过错的影响，不论标的物的灭失由哪一方造成，买受人均须进行折价补偿；意外风险所致的标的物毁损灭失场合，买受人仍应承担折价补偿义务，瑕疵给付的风险负担规则不能作为抗辩事由。由于补偿带来的最终结果上的不公正性应当由赔偿损失或者相关制度予以救济。关于折价补偿金额的计算，计算标准应以标的物的客观价值为原则，以当事人在合同中约定的价款为例外，计算时点应认定为折价补偿请求权成立之日。

Discount compensation refers to the restoration of the property relationship between the parties in the form of money to the state before the civil legal act was performed, and is one of the legal consequences of the invalidity of the legal act established by Article 157 of the Civil Code. Among these issues, the nature, elements, defenses and calculation of the amount of discount compensation are worthy of in-depth study.The provisions of Article 157 of the Civil Code on discount compensation are special provisions under the system of unjust enrichment claims, and the interpretation of the specific rules of discount compensation should be carried out within the framework of the system of unjust enrichment. In the contract of sale, the claim of discount compensation mainly occurs in the case of destruction and loss of the subject matter and resale to a third party. The subject of the discount compensation is the parties to the sale contract, and the obligor is generally the buyer. After the loss of the subject matter of the sale contract, the buyer of the insurance, compensation, compensation should belong to the unjust enrichment system under the return of the original category, should not be calculated in accordance with the standard discount compensation; the buyer of the resale consideration belongs to the category of discount compensation, should be calculated in accordance with the standard amount of discount compensation.Regarding the defense of discount compensation, the following controversies exist: whether the obligation of discount compensation is affected by the purpose of the invalid norm, and whether the obligor of discount compensation can defend through the non-existence of the benefit obtained, the destruction and loss of the subject matter attributable to the opposite party or the risk of accident. In this article, the purpose of the invalid norm has limited influence on the obligation of discount compensation, and the parties' obligation of discount compensation may be excluded in the case of illegal breach of custom or when the obligor of discount compensation is a minor; however, the purpose of the relevant norm cannot be used as a defense in the case of fraud, duress and other revocable circumstances. Due to the special nature of the dual contract, Article 986 of the Civil Code cannot be invoked to exclude the obligation to compensate for the discount on the value of the subject matter itself if the good faith buyer does not exist after the destruction or resale of the subject matter. In addition, the scope of the obligation to compensate at a discount is not affected by the fault of the parties for the loss of the subject matter, and the buyer is required to compensate at a discount regardless of which party caused the loss of the subject matter; in the case of loss of the subject matter due to accidental risk, the buyer is still obligated to compensate at a discount, and the rule of risk of defective payment is not a defense. In addition, the injustice of the final result due to the compensation should be remedied by the compensation for damages or the related system.Regarding the calculation of the amount of discount compensation, the calculation standard shall be based on the objective value of the subject property, with the exception of the price agreed by the parties in the contract, and the point of calculation shall be recognized as the date when the right to claim discount compensation is established.