To address the challenge of leak detection and localization in water pipelines for long-distance water supply projects, a test system for water hammer and leak was designed and constructed. Moreover, a numerical model of water hammer and leak coupling considering dynamic friction and viscoelastic effects was established to achieve accurate transient pressure simulation. An analytical model for leak reflection and transmission coefficients was proposed to investigate the influencing parameters of these coefficients, and an experimental system was designed to verify the model’s accuracy. The results of experiments and model analyses indicate that the leak location is positively correlated with the occurrence time of the pressure drop peak; as the number of leak holes increases, the pressure drop shows a “stepwise” increase, and the transient pressure attenuation rate accelerates; the energy dissipation of water hammer waves caused by dynamic friction reduces the reflection coefficient compared to the frictionless condition; the actual wave velocity of viscoelastic pipelines is lower than the theoretical calculation value, leading to an overestimation of the reflection coefficient.