With the continuous optimization of the payment scene, China's e-commerce environment constantly enriches financial innovation actives and the third party payment business has rapidly grown. Simultaneously, along with the third party comes such legal problem as the rights to the use of the accretion of funds and its profits. The healthy growth of the third party payment will be greatly impacted if such issues are not solved properly. This article, based on Alipay as an example, discusses the nature and interest ascription of the accretion of fund. It references the U.S. supervision mode in order to further promote the healthy development of China's third party payment business.