An evaporation gas control system includes: a canister that traps evaporation gas generated in a fuel tank, a fuel tank pressure sensor that measures pressure in the fuel tank, a purge control valve that controls a flow of the evaporation gas, which is trapped in the canister, into a surge tank through a purge line, a charger that supplies intake air from the outside into the surge tank, a check valve installed on the purge line to prevent the evaporation gas in the purge line from flowing back to the canister, and a controller that diagnoses whether the check valve is faulty or not, by monitoring a pressure variation in the fuel tank when the charger and the purge control valve operate.