To handle the effects of single event upsets (SEU), which are common to computers in space radiation environment, a new fault-tolerant system with dual-module redundancy is proposed using dynamic reconfigurable technique of field programmable gate array (FPGA).This system contains detection and backup alternative functions, that is, the self-detection and self-healing functions can be completed, and consequently a system design with low hardware redundancy and high resource utilization can be achieved successfully.So it can not only detect fault but also repair the fault effectively after failure.Hence, this method is especially practical to the dynamically reconfigurable computers based on FPGAs.Design methodology has been verified by Virtex-4 FPGA on Xilinx M1403 development platform.