In order to research the influence of plateau environment on ram-air rudders, the mathematical model of a ram-air rudder was created. Meanwhile, a simulation research based on the mathematical model was conducted, which indicates that the reduction of air source pressure will reduce the precision of oscillation linearization, and the excess of input control signal amplitude will cause rudder saturation, leading to inadequate rudder controlling. The research of this paper concludes that, to ensure the ram-air rudder working in well condition when applied in plateau environment, a close attention should be paid to the pressure of air-source and the range of input control signal amplitude is highly required. Keywords: plateau environment; ram-air rudder; oscillation linearization