In electrified automobiles, wind noise significantly contributes to the overall noise inside the cabin. In particular, underbody airflow is a dominant noise source at low frequencies (less than 500 Hz). However, the wind noise transmission mechanism through a battery electric vehicle (BEV) underbody is complex because the BEV has a battery under the floor panel. Although various types of underbody structures exist for BEVs, in this study, the focus was on an underbody structure with two surfaces as inputs of wind noise sources: the outer surface exposed to the external underbody flow, such as undercover and suspension, and the floor panel, located above the undercover and battery. In this study, aero-vibro-acoustic simulations were performed to clarify the transmission mechanism of the BEV underbody wind noise. The external flow and acoustic fields were simulated using computational fluid dynamics. The vehicle structural vibration and sound fields of the interior and exterior cabin were analyzed using vibroacoustic models consisting of three subsystems modeled by the finite-element or boundary-element method: The first is an underbody structure finite-element model containing a white body, suspension, battery, and undercover; the second is the interior cabin space boundary-element model; the third is the exterior cabin space finite-element model for analyzing acoustic radiation resulting from vehicle structural vibration for the small space between the floor panel and battery, the motor room and the under-vehicle space between the ground and undercover. The analysis results using the vehicle model reveal that the pressure fluctuations acting on the floor panel are more-dominant inputs for cabin noise than those acting on the outer surface. The pressure fluctuation acting on the floor panel is affected by the acoustic mode of the space between the battery and the floor panel.