In this talk, we will have a brief review of preconditioning techniques for numerical solution of incompressible Navier-Stokes Equations. Then we will focus on the analysis of a dimension-wise splitting with selective relaxation (DSSR) preconditioner in solving incompressible Navier-Stokes equations. The unconditional convergence properties and optimal relaxation parameters are analyzed at both the continuous level and algebraic level. Finally, the preconditioner will be explained from the deflation point of view, which provides a clue for developing hybrid direct iterative solvers.