The invention relates to the technical field of a design method of a fault-tolerant system, in particular to a fault-tolerant system based on process redundancy and a design method thereof. The invention provides a fault-tolerant mechanism and strategy based on process redundancy, dual-mode redundancy or multi-mode redundancy is constructed on key processes, inter-process synchronization and other means are adopted to guarantee that redundant processes operate according to the same execution logic, a monitoring system conducts corresponding error processing on different errors, and finally reliability and usability of the system are improved.