  In this paper, we are concerned with the three-dimensional nonhomogeneous
B\'enard system with density-dependent viscosity in bounded domain. The global
well-posedness of strong solution is established, provided that the initial
total mass is suitably small. In particular, the initial velocity and
temperature can be arbitrarily large. Moreover, the exponential decay of strong
solution is also obtained. It is worth noting that the vacuum of initial
density is allowed.
