违约风险是导致银行信贷风险的主要原因,本文中违约风险用违约概率来量化和描述.首先探讨了违约概率的存在对银行期望收益的影响.然后通过把一个普通的含有贷款利率、抵押品和配给量的信贷决策合同γ=(r,C,q)进一步描述为一个含有违约概率s的信贷决策合同γ=(s(r),C,q),并在此基础上建立了含有违约风险参量的信贷决策模型,给出了相应的信贷决策机制和无配给贷款条件下的信贷决策机制,探讨了相应条件下银行拒绝企业贷款申请的条件. The default risk is the main reason leading to the bank’s credit risk. In this paper, the default risk is quantified and described by the default probability.First, the effect of the default probability on the bank’s expected return is discussed.And then, The credit decision contract γ = (r, C, q) of rationing is further described as a credit decision contract γ = (s (r), C, q) with the probability of default S. On the basis of this, The credit decision model of the parameters gives the corresponding credit decision mechanism and the credit decision mechanism under the condition of non-rationed loans, and discusses the conditions that banks reject the enterprise loan application under the corresponding conditions.