In this paper,the reliability calculation models of water delivery pipeline system with setting up communicating tubes are studied by net decomposition method.The calculation results show that the reliability of water delivery pipeline system may be lowered or increased with increment of the communicating tube number,and the influence of reliability variety of tubulation of delivery main pipeline and T branch pipe is a sensitive factor influencing the reliability of the system.Therefore,the research results have the important leading meaning to the design,the choice of subassembly,the construction installation,maintenance management of the water delivery pipeline system,and looking for path with the biggest reliability of the system.