To provide an engine speed control method and system capable not only of decreasing discomfort of drivers and passengers in a driving state of an excessive engine speed but of calibrating the discomfort by a deterministic method.

The system includes a following device block supplying open loop torque (Tol) so as to make an engine speed follow the reference engine speed during a target engine speed; a reference engine speed and a transient speed state; an observing device block which receives a measured engine speed and combustion torque and is made, based on a system model, as a function of an observed engine speed and the measured engine speed that are made as a function of the combustion torque and the measured engine torque, and which supplies the observed resistance torque displaying an estimated value of whole resistance torque acting on a driving shaft of the engine; and a controller block receiving the open loop torque, the reference engine speed, the observed engine speed, and the observed resistance torque (Robs) and supplying the combustion torque (Tcmb). The controller block controls the engine so that driving torque generated in fuel combustion may become equal to the combustion torque cmb.