The method of characteristics was adopted to analyze water level fluctuation existing in Bull-H surge chamber in reservoir-valve pipe system during waterhammer caused by valve closure operation. The Finite Difference Method (FDM) based on the method of characteristics was used to solve numerically the nonlinear two-parameter characteristic equations goving waterhammer. The finite fixed mesh was applied to obtaining the discrete form of the goving equations and discrete flow-field. The temporal trends of the y-directional flow, water level, velocity of water level and head difference for different heights of water in surge chamber, diameters of cylinder, cutting angles of surge chamber, lengths of horizontal cylinder and lengths of inclined cylinder were obtained under the condition that the air in surge chamber is compressible. The conclusions on water level fluctuation in Bull-H surge chamber were given based on the analyses of the obtained transient numerical results. These conclusions can play a guiding role in designing pipe system and executing surge suppression.