DSP may face with multiple failures in the online upgrade process, so this paper improves the underlying program which uses the method of copying the upgraded program to the Flash backup sector in order to ensure the integrity of the original application function. This paper mainly introduces the basic idea and implementation steps of the online upgrade, expounds the interaction between the host computer and the lower computer, and gives the key code of the program moving on different sectors of the Flash.Finally,by the analyzing of the three kinds of abnormal upgrading,the results show that the method can guarantee the selfrepair and normal operation when the accident happened during the upgrade process.So this method can fully improve the maintainability and faulttolerant of embedded system, it can be widely used in the online upgrade of equipment.