The daily deficiency in debt management based on cash flow model is analyzed.Then,two questions facing enterprise's financial policymaker are put forward.They are: when the supposed enterprise's future cash flow follows different distributions,how much initial cash or receivable account kept by an enterprise is suitable;and while giving definitely the initial cash or receivable account how much borrowed debt is suitable.Therefore,the concept of duty insurance is introduced.Based on the method of option pricing, the relevant parameters solutions are provided,and the key values mentioned in the above two questions are found aut.An example is introduced for illustration.