A power network partition method based on power flow tracing and agglomerative algorithm is proposed.Through reactive power flow tracing，the method can be used to identify the reactive power from each source to each load and hence quantify the degree of reactive power coupling between different nodes，and the distance between nodes can be thus defined.Agglomerative algorithm is then used to aggregate nodes and the best number of partition can be identified.The method is validated through case studies using the IEEE39-bus and IEEE118-bus system.The obtained partition can ensure a basically balanced reactive power within each area and change as system operation condition changes.The method has high computational efficiency and hence has the potential of practical application.