The main analysis tool of KMV model is expected default probability, which refers to the probability of default of the trusted enterprise in the planning period under normal market conditions. The default here is defined as that the fiduciary can not normally pay the principal and interest due, and it is considered that it will occur when the market value of the enterprise is equal to the level of the enterprise's liabilities. Therefore, even if the enterprise sells all its assets, it can not perform all the repayment obligations, so the concept of default will occur.