In this paper, we propose a coupled system that describes the interaction between the Relativistic-Cucker-Smale model and the incompressible Navier-Stokes equations by means of a drag force and establish a theory of global existence, as well as the time-asymptotic behavior of the proposed model in T 3 . It is shown that the coupled system exhibits an exponential alignment under some specific assumptions, and that weak solutions exist globally for general initial data.