Abstract: The top-mounted inlet is designed for a flying wing UAV. By utilizing a specific centerline distribution and area distribution, a S-shaped inlet with large offset and short diffuser is presented. Furthermore, sufficient considerations of the stealth behavior are taken into account in the inlet design. Through CFD and wind tunnel test, the performances of the inlet are obtained, including the effects of free stream of Mach number, the attack angle and the yaw angle. From the flow fields, we can find that the corner vortexs occure in the corner of M shaped inlet, but when airflow flows downstream, the vortexs will disappear gradually. Because of swirl of S duct, the low power energy zone will gradually keep away from the symmetry. Results also show that the inlet is of good performance with the total pressure recovery coefficient greater than 0.98. Based on the research, more experiences are supplied in the design and application of this type inlet.