Based on hydrodynamic lubrication theory, a mathematical model of grinding fluid field in flood is sets up in this paper. Hydrodynamic pressure and velocity of grinding fluid are calculated by multigrid method. Additionally, crude model about the coarseness of grinding wheel and workpiece is built on the basis of slick model and solutions are obtained by multigrid method. Solutions of slick model and crude model are compared. Result shows that the solution of slick model is in good agreement with the crude model and verifies the experimental analysis.