In order to effectively balance the risks of upstream and downstream hydropower stations and the peak load dispatching hydropower station, and reasonably share their benefits, we considered the effects of flood regulation and the storage process of the upstream station as a cooperative risk benefit and used the least core method in cooperative games to establish a least core model of diversion risk benefit sharing under the conditions of the construction of cascade hydropower stations, in order to calculate the diversion risk benefit sharing quota. A case study shows that the sharing of the diversion system and the pumped storage hydropower station exhibited negative values due to the benefits from the water diversion and flood storage at the upstream station, which means that we need to compensate the upstream hydropower station. The sharing of expenses of all the three hydropower stations varied with the change of diversion standards.