On the basis of supply chain finance theory, introduces the upstream core enterprises’guarantee behavior and constructs the model of 3PL inventory financing decision making behavior under the unified credit mode. The research results show that the expected financing profit of 3PL and the loan-to-value ratio of inventory financing are positively related to the core enterprise’s buy-back ratio and the repurchase price. Points out 3PL’s different financing decisions under the constraint of practical market demand, and explains the necessity of guarantee from upstream core enterprise under unified credit mode.