Abstract: The restriction of topographical conditions makes the open channel network become a new way to connect cascade hydropower stations. However, this arrangement has many problems such as complex pipe network, pressure-free coupling and so on. In this paper, the improved pressure gradient method and the global matrix method of open channel network are used to calculate the steady flow and unsteady flow of the hydropower station respectively, and the differences of transient in open channel network between the forward-in and side-out scheme and the forward-in and side-out scheme are discussed. The results show that under steady flow conditions, the forward-in and sideout scheme make the longitudinal open channel in the open channel network play the role of water storage, and the transverse open channel delivers water to the downstream power station. In the forward-in and side-out scheme, the longitudinal pipeline conveys water to the downstream power station and the transverse pipeline distributes the flow. Under the load rejection or load-up condition of the downstream power station, the wave in the forward-in and side-out scheme propagates along the transverse pipeline and to the longitudinal pipelines on both sides when the fork point is passed through. In the forward-in and side-out scheme, the wave propagates along the longitudinal pipeline.When the fork point is passed through, as the water depth increases, the wave propagates from the transverse pipeline far away from the upstream to the transverse pipelines on both sides.