This study analyzed various possibilities of flash fire which could occur in a variety of combats, in order to predict that of flash fire of combat system armor using Autodyn program. The possibility was judged by the temperature distribution of fuels, which was caused by the impact of parts of fuel systems through an armor, in the event of getting shot by external ammunition. Diverse variables could affect the possibility of flash fire: external ammunition(Type A: penetration 570 mm, Type B: penetration 410 mm), fuels(Gasoline, Diesel, Kerosene), the thickness of an armor(100, 200, 300, 400, 500 mm), the gap of a fuel tank and an armor(45, 95, 145, 195, 245, 295 mm). As a result, when an armor was 20 mm think, the temperature of 3 fuels ranged like this: Gasoline 372~387 K, Diesel 442~408 K, Kerosene 384~395 K. Although they made a little difference among them, they all didn't reach their ignition points. When an armor was 200 mm think, each fuel reached the maximum temperature, not reaching its ignition points as well. The thicker an armor was, the lower the temperature got. When Type B ammunition was used, the temperature of fuels went up 19~59 K higher than Type A was used. In the case that the gap of fuel tank and an armor was 20 mm thick, the temperature distribution of Gasoline showed 389~450 K, the maximum temperature appeared in the gap of 145 mm, and the minimum temperature 295 mm. For Type B, the temperature distribution of fuels ranged 386~401 K, the maximum temperature appeared in the gap of 245 mm, and the minimum temperature 45 mm. There was no significant difference between two cases, and neither of them reached its ignition point. Accordingly, as the tested fuels of combat systems didn't reach their ignition points, it is thought that the possibility of flash point of an armor is low.