The fly-wing UAVs have large individual difference, a large number of control surfaces, short longitudinal control lever and static instable heading. To solve the problems, this paper presents a direct allocation method from angular acceleration to the control surface, and a control law taking angular acceleration as the control instruction. First of all, the angular acceleration is directly allocated to the control surfaces that have been graded in discrete state. Taking the angular acceleration as control instruction, a longitudinal Robustness Servomechanism Linear Quadratic Regulator (RSLQR) control law, and a lateral stabilization control law, are designed. The simulation results for the sample UAV under nonlinear condition show that: 1) The angular acceleration allocated to the control surface satisfies the distributed precision requirement; and 2) The control law with the angular acceleration as control instruction has high tracking accuracy and satisfies the speed requirement.