In this research, both reservoir simulation and well testing were employed to investigate the average reservoir pressure in the Xing 1-2, a multilayer sandstone reservoir. The concrete methods included the well testing, Peaceman, and volumetric weighted average method (VWA). The average reservoir pressures for the last three years of the monitoring wells were calculated. The results showed diversities among three methods at each well pattern. The factors which caused diversities in three methods have been categorized, like the geological uncertainties, production impact, the difference in mathematical methods, etc. The wells in low pressure zones were detected and analyzed. By reducing the influence of referenceless interpretations, the system provided more accurate interpretations. The results were also used to optimize the monitored wells and to offer reference for the improvement of the injection and production system.