To investigate the process fluctuation influence on SRAM(static random-access memory) single event upset in sub-20 nm FinFET(fin field-effect transistor) process, a high precision three dimensional technology computer-aid design model based on commercial process fluctuations was established, then simulated to find the FinFET SRAM single event upset threshold under different process corners. The simulation results show that the FinFET SRAM upset threshold has less variation induced by process corner fluctuation. Meanwhile, the sensitive positions of SRAM are on the N-complementary metal oxide semiconductor. Then, to understand the the impact of specific process parameter fluctuations on the single event upset threshold, the process fluctuation factor impact on single event upset was discussed, including fin width, fin height, the oxide thickness and the work function fluctuation. The simulation results show that the first two factors did not affect the upset threshold, while the latter two factors caused slight fluctuations in the upset threshold. Significant reduction in the impact of process fluctuations on FinFET SRAM single event upset threshold is firstly found, which is of great significance for the development of highly consistent radiation hardened aerospace integrated circuits.