This paper investigates the state-tracking control problem in conversion mode of a tilt-rotor aircraft with a switching modeling method and a smooth interpolation technique. Based on the nonlinear model of the conversion mode, a switched linear model is developed by using the Jacobian linearization method and designing the switching signal based on the mast angle. Furthermore, an H_∞ state-tracking control scheme is designed to deal with the conversion mode control issue. Moreover, instead of limiting the amplitude of control inputs, a smooth interpolation method is developed to create bumpless performance. Finally, the XV-15 tilt-rotor aircraft is chosen as a prototype to illustrate the effectiveness of this developed control method.