Abstract: The definition of nonlinear control sysms on fibre bundles proposed by Brockett and Willems is incomplete from the mathematical view geometric framework is proposed and a minimal realization theory is developed for nonlinear control systems on fibre bundles which is elaborated as a natural generalization of Sussmann’s theory and differs essentially from Van der Schaft’s approach. Limitations of realization theory given by Van der Schaft are also discussed.