A synchronization control method includes controlling an engine speed to follow a motor speed as a target speed of the engine when synchronization between the engine speed and the motor speed starts according to a demand for the lock-up of the engine clutch while travelling under the EV mode with the engine clutch opened; estimating the engine speed at a time of a transmission gear ratio change at which the motor speed increases and reaches a preset motor speed, wherein the transmission gear ratio change is carried out at the preset motor speed; calculating the motor speed, which is reduced after the transmission gear ratio change, by using the preset motor speed and information on a gear ratio before and after the transmission gear ratio change; and controlling the engine speed by resetting the target speed to the calculated motor speed as a new target speed of the engine.