The article introduces the concept and principle of the timeout service, and elaborates on how to design it in the sequential operations and task operations during the programming for MCU (Micro-Controller Unit). In virtue of interrupt mechanism, it needs just a few inner resources to realize. It can resolve the incidents that the program can't exit from the function modules because of the unsatisfied conditions, engrossing the MCU’s time or overlapping the tasks’ same variables in the multi-task architecture, so as to appear dead loop or running errors due to the mutual interference among the resources. Therefore, the timeout service enhances the redundancy and the reliability of the embedded system.