Water hammer is common in nuclear engineering pipeline systems, such as feedwater systems, essential service water systems and passive residual heat removal systems, etc. Water hammer can cause a large fluctuation of fluid pressure, posing a threat to the normal operation of pipeline systems, so it is necessary to reduce the pressure fluctuation and energy. The flow resistance components such as the orifice plate are the key parts to mitigate the influence of water hammer. For the reservoir-pipe-valve (RPV) system, a water hammer model that considered the effect of unsteady friction was established and solved by the method of characteristics. The calculation results of theoretical model agreed well with the experimental results. On this basis, the orifice plate was added to analyze its influence on the transient flow process. Based on the traditional analysis method and energy analysis method, the dissipation effects of the frictional resistance and the local resistance of pipeline system were studied. The analysis results show that as the orifice plate moves from upstream to downstream of pipeline system, the fluctuation of internal energy and kinetic energy decreases, the orifice dissipation work increases, and the friction dissipation work decreases. The research results show the advantage of energy analysis method and provide guidance for the design of energy dissipation equipment.