This paper proposes an energy-efficient trajectory planning method for a wheeled robot in slope ascending scenario. This method basically exploits a power consumption model of the robot which is obtained from the following two phases: first, the values of the robot power consumption in different slope angle, robot velocity, and robot heading angle are numerically calculated using a dynamic simulation of the robot taking into account of an accurate wheel-soil interaction mechanics; and subsequently, an approximated model for the robot power consumption is elaborated by neural network. Using the power consumption model an energy-efficient trajectory for a slope traversal case can be generated. Here, a bezier curve is used to provide a smooth trajectory designed with an appropriate arrival time as well as the control points for the curve. The numerical simulation result of the trajectory planning based on the proposed method gives several insights for a feasible trajectory for slope ascending scenario.