Abstract: As a lowvelocity aircraft, the stratosphere airship has a high sensibility to wind disturbance, so it costs much energy for long distance cruising horizontally against the wind. Aiming at minimum energy consumption, a trajectory optimization method for stratosphere airship is proposed by using the singular perturbation method. Firstly, the wind field coordinate system is established for converting the process of airship cruising to desired destination into a similar optimal interception problem. According to the behaviors of state variables of airship, and using proportional navigation guidance, three time-scale separations are established and the mathematical model of the singular perturbation is set up. Then, analytical solutions are derived by solving the corresponding three sub-problems. Finally, a numerical simulation is carried out. The result shows that the proposed trajectory optimization method is efficient for stratosphere airship and has some certain applications in engineering.