Given solenoidal vector u 0 ∈Ḣ −2δ ∩ H 1 (R 2 ), ρ 0 − 1 ∈ L 2 (R 2 ), and ρ 0 ∈ L ∞ ∩Ẇ 1,r (R 2 ) with a positive lower bound for δ ∈ (0, 1 2 ) and 2 < r < 2 1−2δ , we prove that 2-D incompressible inhomogeneous Navier-Stokes system (1.1) has a unique global solution provided that the viscous coefficient μ(ρ 0 ) is close enough to 1 in the L ∞ norm compared to the size of δ and the norms of the initial data. With smoother initial data, we can prove the propagation of regularities for such solutions. Furthermore, for 1 < p < 4, if (ρ 0 − 1, u 0 ) belongs to the critical Besov spaces Ḃ 2 p p,1 (R 2 ) × Ḃ −1+ 2 p p,1 ∩ L 2 (R 2 ) and the Ḃ 2 p p,1 (R 2 ) norm of ρ 0 − 1 is sufficiently small compared to the exponential of u 0 2 L 2 + u 0 Ḃ −1+ 2 p p,1 , we prove the global well-posedness of (1.1) in the scaling invariant spaces. Finally for initial data in the almost critical Besov spaces, we prove the global well-posedness of (1.1) under the assumption that the L ∞ norm of ρ 0 − 1 is sufficiently small.