A dynamic characteristic of a hydraulic pressure is significantly enhanced since a line pressure control system. A method employed by the system includes determining whether a vehicle is in a power-on state, determining whether a damper clutch is being engaged when the vehicle is in the power-on state, compensating a line pressure duty determined on the basis of an engine torque with a first compensation duty determined on the basis of a vehicle speed and an operation state of the damper clutch when the damper clutch is being engaged under the power-on state, and controlling the line pressure according to the compensated line pressure duty.