This paper uses the technology of topology searching to dynamic modeling for hydropower auxiliary system, puts forward the topology searching algorithm applicable to the auxiliary pipe network system, and establishes the pipe network component model suitable for the dynamic calculations, uses the results of topology searching to integrate the pipeline loop appropriate to calculation, and establishes corresponding dynamic equations of the pipe network in the model. A linear theory is applied to convert the mutual coupling non-linear equations into linear equations for solving it iteratively. This algorithm is very efficient and can adapt to the complex changes of pipe network and components working conditions. Its calculation model can reflect the changing processes of the auxiliary components among different states. Topology searching algorithm can deal with the isolating branch well, effectively avoid the problems of isolating nodes and sub-network in the pipe network calculations. Its algorithms and models have been applied in a real large hydropower simulation system, which validates the effectiveness of this algorithms and models.