In large-scale systems such as satellites, timer is the key component for triggering synchronized operations across all units. The precision and stability of timer is critical to the success of the entire system. Space radiation effects, particularly Total Ionizing Dose (TID) effects and Single Event Effects (SEE), may induce timing sequence disruptions, consequently causing operational anomalies throughout the entire system. This paper designs and implements a high-reliability, radiation-hardened timer approach based on FPGA. The design incorporates multiple protective measures, including program memory TMR, timed refresh, critical parameter anomaly protection, software TMR, and timer pulse-width protection. These strategies collectively ensure the reliable operation of the timer within the space radiation environment.