Compared with traditional radiant cooling systems, decoupled radiant cooling systems have stronger anti-condensation ability and cooling capacity. Since a decoupled radiant cooling system removes sensible loads only, it needs to be paired with a ventilation system to remove latent loads. This study proposed a ventilation-integrated decoupled radiant cooling system (ViDRCS) and explored its thermal performance using computational fluid dynamics (CFD) technology. The results showed that as the supply air velocity increased, the convective and total heat flux grew slightly, while the radiative heat flux remained unchanged. The minimum and average temperature of the membrane increased significantly, which will further benefit the condensation prevention. The thermal environment created by the ViDRCS was also investigated. This study can provide theoretical guidance for the practical application of the ventilation-integrated decoupled radiant cooling system.