Abstract: The similarity between fluid mechanism and electromagnetics leads to the similarity between the governing equations of steady fluid flow, electrostatic field and static magnetic field, and there are some similar rules in numerical calculation. All these equations are expressed in terms of convection, diffusion and source, and the numerical method in computational fluid mechanics can be used to calculate the electromagnetic field equations. Based on the analysis of both the mathematic and physical meanings of upwind (or downwind) scheme and forward (or backward) difference scheme, it is suggested that the upwind and downwind schemes are available to solve the equations involving electric charge movement, and the upwind scheme available to solve the equations for fluid flow.