Applying robust control design methods to large envelope flight control law of aircraft whose model parameter varies greatly with flight condition was studied in this paper. Representation of time domain based uncertainty of state space model and representation of frequency domain based uncertainty of transfer function matrix model were conducted respectively. A linear fraction transformation form that uses interpolation was presented. A robust lateral direction flight control law was designed for certain aircraft. The simulation results show the control system is stable and performance robust, which proves effectiveness of the method.