This study proposes a novel method for designing an integrated absorption-transmission flexible ultrathin electromagnetic window, which can absorb the unpolarized incident waves over a wide range of angles and is almost transparent at a given frequency band. The experimental results demonstrate 93% absorption at 4.46 GHz and 98% transmittance at 2.86 GHz, indicating an insertion loss of 0.09 dB. The total sample thickness is 0.288 mm, which makes the structure flexible and easy to conform to the curved target. Furthermore, a method for designing a broadband-integrated absorption-transmission electromagnetic window is proposed. The simulation results denote that the absorption can reach 90% at 7.7-12.2 GHz and that the transmittance is 90% at 4.35 GHz. The proposed broadband structure performs appropriately over a wide range of incident angles.