Abstract: Auctions are common in everyday life and have penetrated into all areas of online markets, including supply chain procurement, resource allocation, and online e-commerce transactions. In recent years, the auction theory has also been extended to online peer-to-peer (P2P) lending markets for analyzing the interests of lenders and borrower. However, many related researches on online P2P lending markets of China mainly focuse on risk control, behavior decision, trust and supervision. Fewer literatures explore China's online P2P lending trading mechanisms through the auction theory. Therefore, the existing deficiencies of trading mechanisms of China's online P2P lending markets are mainly analyzed, and the current trading mechanisms are improved through the auction theory. In this process, a lending contract is first set up to determine the initial loan demand, then two open-descending closed auction mechanisms on online P2P lending markets are designed, which include pre-symmetric and asymmetric auction models. This paper shows that a variation of the standard open-descending auction is an optimal mechanism for the borrower. These two mechanisms will consist of two stages (both take place before the borrower's demand realizes). In Stage 1, the borrower will run a standard open-descending auction for an initial fixed quantity. In Stage 2, the winning lenders from Stage 1 will receive one additional offer from the borrower to supply more units at unit prices no higher than the auction's ending price. Results show that these two mechanisms are optimal for borrower; and borrower and lenders are more familiar with these simple auctions. Therefore, it can be used to improve China's trading mechanisms of online P2P lending markets. Results of examples analysis also show that, as long as trading mechanisms of online P2P lending markets can be normally operated, these two open-descending closed auction mechanisms can further reduce the borrower's payment cost. And these mechanisms can be an effective improvement scheme compared with the trading mechanism provided by China's existing auction platform, which is conducive to the healthy development of China's P2P lending markets.

Key words: online P2P lending, closed auctions, open-descending auctions, stochastic loan demand