不当得利之债,是指没有合法根据,取得不当利益,造成他人损失的,应当将取得的不当利益返还受损失的人。在不当得利争议中,主要争议当事人受益方和受损方之间举证责任应如何分配,在双方都不能提供充分证据时又该如何运用高度盖然性证明标准认定案件事实,在司法实践中存在一定的争议,也直接关系到了不当得利制度价值理念的体现和功能的发挥。【案情简介】原告张某诉称,原告于2009年5月17日从其银行卡上转账40万元到被告在中国银行某支行的银行卡内,有银行转账单作为凭据。此后,原告因资金周转困难,要求被告归还此款,被告不同意归还。为此, Unfavorable profits of debt, refers to the absence of legal basis, to obtain improper benefits, causing losses to others, should be returned to the loser of the improper benefits. In the dispute over unjust enrichment, how to allocate the burden of proof between the beneficiary and the injured party of the main dispute parties, and how to use the high probabilities to prove the facts of the case when both parties can not provide enough evidence exist in the judicial practice Controversy, but also directly related to the value of the system of unjust enrichment reflects the concept and function. 【Brief introduction of the case】 Zhang complained that the plaintiff, on May 17, 2009, the plaintiff transferred 400,000 yuan from his bank card to the defendant in a bank branch of Bank of China with a bank transfer bill as a voucher. Since then, the plaintiff due to cash flow difficulties, requiring the defendant to return this paragraph, the defendant did not agree to return. to this end,