Abstarct: The supersonic air intakes that are installed on the side of the wing or body of an aircraft, are exposed to the low-energy boundary laxyer air flow, which is prevented from entering this type of air flow by using one of the boundary laxyer control methods called diverter. When the mass flow rate to the intake is lower than the design point, the boundary laxyer in front of the intake grows rapidly and apt to separate due to the increase of adverse pressure. If an aircraft fly in a supersonic speed, the shock and boundary laxyer interaction cause the boundary laxyer to separate from the surface. If the boundary laxyer grows higher than diverter height, some portion of the boundary laxyer would flow into the intake. When the low momentum energy boundary laxyer flow is introduced to the intake, not only the total pressure at the engine face becomes lower but also the pressure distortion, after mixed with undisturbed high velocity flow outside of the boundary laxyer, becomes higher and eventually leads to the intake instability. In this research, due to the lack of sufficient information in the references, the attempt is to firstly investigate the intake performance in two-dimensional and three-dimensional mode with the help of the geometry of a specified type of supersonic intake of the external compression type with a ramp compression surface. Then, the effect of using one of the flow boundary laxyer control methods called diverter in the three-dimensional intake with three different heights (0.02, 0.04 and 0.06 meters) will be modeled and analyzed. It is expected that the output of this research will provide the possibility of improving the performance of the air intake with the least amount of disadvantages (increased pressure drop and distortion). The results showed that with the increase of the diverter height, the distortion coefficient, pressure recovery decreases and the drag coefficient increase and vice versa. So, adequate boundary laxyer diverter height should be selected after considering aircraft maneuver envelope, flight speed, and mass flow rate of the intake.