A method for correcting an air-fuel ratio deviation for each cylinder in an engine of a vehicle includes measuring a signal of an oxygen sensor mounted on an exhaust pipe of the vehicle using a low-pass filter and a moving-average filter; calculating an oxygen sensor roughness based on the measured signal of the oxygen sensor modulating a fuel injection amount of fuel injected into each cylinder in the engine; detecting a variation of the oxygen sensor roughness according to the modulated fuel injection amount; determining an optimal fuel injection amount based on a relationship between the fuel injection amount and the oxygen sensor roughness; performing fuel injection amount control based on the determined optimal fuel injection amount to correct the air-fuel ratio deviation for each cylinder.