Multi-location comparison is needed when towers have to be installed in the river floodplains for UHV transmission lines. The surface water modeling system (SMS) is used to analyze the flow field distribution on the floodplain under design flood, based on which the towers location for large-span transmission lines are selected and assessed. The calculation results of SMS are direct, reasonable and can provide a good basis for choosing the tower locations in floodplain where the flow is small, the scouring depth is small and the tower has little impact on flood passage.