Computing accuracy in large CFD problems is restricted by the computation cost. A hydraulic modelling platform (HydroMP) was constructed using computing cloud to reduce costs and to provide a uniform interface between the dataset and the model for hydraulic models. This paper gives a generic integration method for hydraulic models and a scheduling mode for the cloud computing. The system includes the models and computing resources, including the data interface, model calls and interactions and computations of resource allocation using Web Services, XML(Extensible Markup Language) and OpenMI(Open Model Interface). This design assures that the cloud computing platform can conveniently call the models, exchange data between the servers and the clients, and dynamically allocate the computing resources including multiple cores and multiple nodes. The platform with the integrated flow model is used to analyze the hydraulic response to a change in the discharge of the South-to-North Water Diversion Project, which is a multi-client, multi-level and multi-scheme simulation. The results indicate that this model improves the computational efficiency and compatibility. This hydraulic computing model based on cloud computing theory allows multiple schemes be solved simultaneously using multiple clients in a WAN Internet and multiple users. The cloud computing model lowers the threshold for using HPC resources and improves the utilization efficiency of computation resources.