The functionality of vehicle system controller for a powersplit powertrain hybrid electric vehicle is described and a finite graph is given to represent the transition relations between the different vehicle driving modes in this paper.In order to speed up the calculation,an innovative and simplified dynamic programming method is proposed to reduce the calculation grids caused by the discretization.The calculation results from the dynamic programming are analyzed and used to obtain the transition rules among different vehicle driving modes for a powersplit powertrian hybrid electric vehicle.