Conventional method of flood delivering coolant fluid by a nozzle in order to achieve high process performance. However, hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect between wheel peripheral surface and work surface. In the paper, theoretical hydrodynamic pressure modeling were presented for flow of coolant fluid through the grinding zone in flood delivery grinding using smooth and roughness surface grinding wheel respectively. The simulation results show that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and work surface and the maximum pressure value was generated just in the minimum gap region in which higher fluid pressure gradient occuring. It can also be concluded the surface roughness of grinding wheel and workpiece makes the contact zone’s hydrodynamic pressure rough and unstable, i.e. the value curve considering roughness is not smooth, leading to the micro-elastohydrodynamic lubrication phenomenon.