Nowadays, trade credit (permissible delay in payment) is one of the most important source of short-term external financing for firms in a broad range of industries and economies. This paper considers a supply chain for deteriorating items including a supplier and multi retailers. In this model, the supplier offers all retailers a permissible delay of payments in settling their accounts, and each retailer has two types of customers. One of the customers is the ultimate customer who pay for the items up on receiving them, while the other is the intermediate customer or trade customer who requires some period of time within which to settle for the goods supplied to them. Therefore, how to control inventories of deteriorating items, and achieve the maximum time value of money becomes an important problem for each retailer. We introduce the deteriorating inventory model with partial trade credit policy under independent and cooperative purchase, respectively. Then the cost allocation problem arising from the cooperative purchasing is considered and formulated as the cost allocation game with two-level trade credit. It is proved that the cooperative purchasing not only leads to a decrease in each retailer's cost but also an increase in the frequency of replenishment, which in turn reduces the loss of decay.