A method of controlling a DCT (double clutch transmission) of a vehicle to conduct a series of downshifting operations from a preceding gear to a subsequent gear via a current gear in response to deceleration of the vehicle may include slip-controlling, continuously, a clutch which has been in an engaged state in the preceding gear, at least until a shift gear of the subsequent gear is engaged, wherein the slip-controlling includes maintaining the engaged state of the clutch with the current gear.