A method of controlling a transmission (e.g., CVT) comprises dividing the entire range of an input torque to a transmission from an engine into a plurality of partial torque ranges; setting the maximum torque of the respective partial torque ranges as a representative torque of the respective partial torque ranges; and setting a target hydraulic pressure, which is to be provided to the transmission, according to the representative torque and a predetermined target speed ratio. The method allows a target hydraulic pressure for controlling a transmission to be maintained constant even though an input torque from an engine is changed, and allows the transmission to maintain a speed ratio constant, thereby ensure a stable and smooth ride.