Abstract: As a core component of the air-sea integrated communication system, channel modeling for Unmanned Aerial Vehicle (UAV)-to-sea (U2S) communication is crucial to system design. Targeting practical propagation scenarios, this paper proposes a channel model suitable for U2S Multiple-Input Multiple-Output (MIMO) communication, which consists of a line-of-sight (LoS) path and multiple random scattering paths. In the modeling of scattering paths, emphasis is placed on the effects of scattering sources such as waves in the surrounding sea areas. To characterize dynamic attitude changes such as the 3D rotation of UAVs in the air and the rolling of ships around their forward direction, a time-varying attitude matrix is introduced to update the position vectors of scatterers and transmitting antennas in real time. On this basis, the paper analyzes the core Doppler effect of the channel, including Doppler shift, Auto-correlation function, and Doppler power spectrum density. Finally, the effectiveness of the proposed model is verified through simulation experiments. This model can provide theoretical support for the design and optimization of air-sea integrated communication systems.