Urban water supply network is a modern urban survival and development of the infrastructure of a city,and its normal running conditions have important significance. The actual hydraulic process in the variableload water distribution networks can be treated as the slow transient flow which belongs to the unsteady flow. This paper analyzes the multi-loops network slow transient model based on graph theory,and the link flow matrix is treated as the variables of the discrete solution model to simulate the process of the slow transient flow in the network. With the simulation of hydraulic regime in an actual pipe network,the changing laws of the flow in the pipes,nodal hydraulic heads and other hydraulic factors with the passage of time are obtained. Since the transient processes offer much more information than a steady process,the slow transient theory is not only practical on analyzing the hydraulic condition of the network,but also on identifying hydraulic resistance coefficients of pipes and detecting the leakage in networks. Urban water supply network is a modern urban survival and development of the infrastructure of a city, and its normal running conditions have important significance. The actual hydraulic process in the variable load water distribution networks can be treated as the slow transient flow which belongs to the unsteady flow. This paper analyzes the multi-loops network slow transient model based on graph theory, and the link flow matrix is ​​treated as the variables of the discrete solution model to simulate the process of the slow transient flow in the network. With the simulation of hydraulic regime in an actual pipe network, the changing laws of the flow in the pipes, nodal hydraulic heads and other hydraulic factors with the passage of time are obtained. Since the transient processes offer an additional information than a steady transient network is not only practical on analyzing the hydraulic condition of the network, but also on hydraulic pressure coefficients of pip es and detecting the leakage in networks.