In this paper, we first prove the local well-posedness of the 2-D incompressible Navier–Stokes equations with variable viscosity in critical Besov spaces with negative regularity indices, without smallness assumption on the variation of the density. The key is to prove for p∈(1,4) and that the solution mapping d4561d7a8623c2ec6d89c8b74d35" title="Click to view the MathML source">Ha:F↦∇Π to the 2-D elliptic equation is bounded on . More precisely, we prove that
The proof of the uniqueness of solution to (1.2) relies on a Lagrangian approach , and . When the viscosity coefficient μ(ρ) is a positive constant, we prove that (1.2) is globally well-posed.