Flow control for high-altitude airship based on synthetic jet was studied by a numerical simulation. The synthetic jet was arranged along primary separation lines on the surface of the airship. The synthetic jet was injected into boundary layers around the airship through slots on the wall to generate vortex flows, thus delaying flow separation, reducing drag and mitigating gust at high angles of attack. The original airship was first simulated to find the locations of the primary separation lines; the variation of the airship"s drag coefficient was subsequently studied with various amplitudes of the synthetic jet. Based on these, the flow control effect of the synthetic jet is further analyzed. The results show that greater suction velocities have larger reduction in the time-averaged drag, but with a cost of more energy consumption and larger fluctuations of aerodynamic forces. After deducting energy consumption of the synthetic jet, the optimal time-averaged control was achieved at about 30 degrees angles of attack. The study indicates that synthetic jets can be used to reduce a cruise drag of the airship at lower angle of attack and to mitigate a gust by controlling transient aerodynamic forces at higher angle of attack.