Abstract: Aimed at the characteristics of the second phase of Xi'an hydropower station，and on the basis of the Specifications for Construction Planning of Water Resources and Hydropower Engineering(SL303-2004)，this paper determined the diversion standards of the dam construction project，and came up with three diversion schemes：once-in-a-decade flood standard for all year round，once-in-a-decade flood standard for non-flood season and the water flow through the dam body，once-in-a-decade flood standard for non-flood season and the water doesn't flow through the dam body，and then makes comparison and selection of these three schemes and finally determined using the non-flood season and the water doesn't flow through the dam body.