The augmented flight dynamic model for trajectory optimization is built to improve the optimal control strategy of trajectory optimization for tilt-rotor aircraft landing in short takeoff after one engine failure. The longitudinal rigid-body flight dynamic model is augmented with a set of algebra equations describing the relationship between the aerodynamic forces and controls in the cockpit, and a set of differential equations describing the control rates to avoid jump discontinuities of controls in the trajectory optimization. The trajectory optimization problem is transformed into a nonlinear programming problem and solved by a sparse sequential quadratic programming. The XV-15 tilt-rotor aircraft is taken as a sample for the investigation. The optimal solutions are calculated and compared with those obtained in the relevant reference. The results indicate that the augmented flight dynamic model can provide more longitudinal control information such as the collective control input, the root collective pitch, the longitudinal cycle pitch and the rates of control variables. In addition, the time histories of power required, thrust coefficient and longitudinal stick are more relatively gentle. Therefore, the presented method can provide pilots more useful references to perform the landing procedure.