The decision-making contract is described as a function of price, credit limit, and guarantee in the situation of variable price. The paper analyzes the creditor’s losses caused by inaccurate judgment of the client’s risk types when there are high and low types of credit risks. According to the above losses, a credit decision model under the effects of the default probability is constructed from the principle of minimization of risk and the model’s Kuhn Tucker -conditions are given in the paper. And credit sale decision mechanism with guarantee and credit sale risk decision mechanism without guarantee are given respectively in the paper. At the same time the influences of credit limit, price and guarantee on credit risk under the above decision mechanism are analyzed.