In this paper, we focus on the global well-posedness of solutions to three-dimensional incompressible Boussinesq equations with temperature-dependent viscosity under the smallness assumption of initial velocity fields $u_0$ in the critical space $\dot_{B}_{3,1}^0$. The key ingredients here lie in the decomposition of the velocity fields and the regularity theory of the Stokes system, which are crucial to get rid of the smallness restricition of the initial temperature $ heta_0$. In addition, we mention that the improved decay estimates in time is also necessary.