The Unmanned Aerial Vehicle (UAV) has special dynamical characteristics in ground motion different from that of flight in the airborne. The forces and moments on the ground to the UAV differ during taxiing, according to the different mechanical and aerodynamic characteristics. An all-states nonlinear model is established by studying on a sample UAV. Rotation speed and lift off speed is determined, finally a control law including longitudinal and lateral control for automatic take-off is designed. Results of simulation show that the model and control scheme can not only join the ground taxiing and flight in the airborne smoothly, but also has a high value in realizing engineering project.