With the construction of the southern regional power market, the scale of cross-provincial and cross-regional power transactions is gradually expanding. In the future, the co-existence of the dual-track system of plan and market is expected to exist for a long time, in which the decomposition of the contracted power is of great significance to the market operation and the interests of the market entities. To better promote the implementation of the scheduling plan of the power generations and ensure the interests of the market entities, a two-stage decomposition method of the preferential power generation plan electricity based on multi-band uncertainty sets of inflow water is proposed. In the first stage of power decomposition, the annual power decomposition model for the wet season and the dry season is established by taking into account the characteristics of inflow water during the wet season and the dry season, so as to realize the seasonal decomposition of the annual power to the month. And then, with the goal of consistency of the power generation progress, a monthly power decomposition to daily model based on the consistency of progress coefficients is established. In the second stage of power decomposition, the uncertainty of inflow water is considered and described as a multi-band uncertainty set, and a two-layer model is used to solve the conservative power decomposition curve under the power decomposition curve of the first stage, starting from the time scale of the monthly power decomposition to the day. Finally, the planned power decomposition curves and conservative power decomposition curves of each station are obtained by decomposing the hydropower stations in Yunnan Province as an example, and the effectiveness of the method proposed is comparatively analyzed.