Airborne laser weapon system can increase the survivability of the aircraft by active defense. In order to obtain longer fire range, a large diameter of the airborne laser weapon turret is required, which may cause negative influence to the aircraft. In this paper, the influence of turret diameter on aerodynamic and stealth performance of the aircraft is analyzed by means of computational fluid dynamics method and physical optics method. And the influence of turret diameter on combat effectiveness is analyzed with agent-based combat simulation. The results show that the increase of turret diameter will lead to a slight decrease of aircraft speed, while the influence quantity of laser turret to aircraft speed is within 2%. In the meantime, the increase of turret diameter increases the front RCS of the aircraft, an diameter of 30cm, 50cm and 70cm of laser turret could lead to an increase of 64%、173% and 282% of the aircraft RCS. The 50cm diameter design could increase the most mission effectiveness, which is 77.2%.