A method of controlling a power train composed of an engine and a transmission is disclosed wherein a control for the engine and a control for the transmission are integrated in a single control program. The method comprises detecting a change in the engine operating state, deciding which one of a plurality of control programs is required for the change in the engine operating state, placing a priority level on the control program decided, and activating the decided control program at a timing scheduled on the priority level in accordance with a predetermined control logic and controlling both the engine and the transmission in an integrated manner.