During carbonate reservoir simulations, more one saturation functions are utilized to characterize the fluid saturation variation. If no more reliable Pc’s curves are applied to calculate initial fluid saturation, poor match quality, the high risks of assessment of modeling the water breakthrough timing, low recovery factor or more convergences are caused. So the Sw log data are classify and ranged, new PC curves and relativity permeability curves are generated. The upscale static water model was divided according to different ranges. The water saturation functions were assigned based on certain SATNUM. The initial water saturation model ensures high quality match of lateral and vertical fluid distribution and excellent match with less volumetric gaps between static model and dynamic model. Uncertainties and risks are reduced effectively while running timings are saved.