In order to overcome the shortage that unmanned air vehicles (UAVs) are easily disturbed by air current and tend to be unstable, a robust controller was developed for a certain small UAV’s lateral motion using quantitative feedback theory (QFT). Firstly, Basically Non-interacting (BNIA) Method was applied to decompose the UAV’s lateral motion into two subsystems. Then QFT approach for LTI/SISO system was used in each subsystem’s controller design respectively. Finally, QFT controller for UAV’s lateral motion was synthesized based on the two subsystems’ QFT controllers. The simulation results show that the QFT robust controller not only improves dynamic characteristics but also enhances stability and robustness.