Abstarct: In large piping systems, a pump is unable to supply the required flow and head. Therefore, the pumps are connected in series and in parallel to provide the required head and discharge. As we know, the power failure of the pumps causes transient flow and changes in the fluid pressure inside the tube, resulting in a dynamic load on the tube structure. Investigating the maximum and minimum pressure caused by water hammer plays an important role in the design of the pumping system. Therefore, the study of fluid-structure interaction (FSI) in these systems is of great importance. The phenomenon of cavitation is also a very important topic due to the destructive effects that can occur in a pipe system. The purpose of this thesis is to present a mathematical model and numerical solution of the problem of fluid-structure interaction due to water hammer after sudden stopping of the parallel pump group in a distribution network considering the liquid column separation phenomenon. Hydraulic equations were solved using the method of characteristic (MOC) and structural equations using finite element method (FEM) in the time domain. On the other hand, the governing relations between the pumps are head equilibrium and torque equations, which were solved using Newton-Raphson numerical method at each time step. Also, for the modeling of the pumping system, the assumptions of homogeneous pumps were used. In this assumption, the pumps are considered the same for the use of characteristic curves of the pump in an unsteady state baxsed on the specific speed. In examining the liquid column separation phenomenon, the simplest method called Discrete Vapour Cavity Model (DVCM) was used to easily integrate it into pumping systems and analyze with interference effects and to investigate its accuracy. According to the results, with increasing number of pumps, the power of the pumping system is also increased, and as a result of a more intense impact, the cavitation is more intense in the stronger pump group. Also, the control valve closing time affects the pressure on the system in interaction analysis and cavitation.