Abstract: To analyze the hydraulic geometries of the middle and lower Songhua River, hydrological data were collected of measured discharge, measured cross section, daily average discharge, and daily average transport rate of suspended load at its seven typical hydrological stations for the period of 1955-1987. Correlation analysis between stage and discharge was used to obtain dominant discharge, dominant stage and dominant channel width, and the cross section of a natural river was generalized using a hydraulic equivalent, compound rectangular cross section and its similarity of stage-discharge relationship and stage-cross sectional area relationship to those of a rectangular weir flow. The results show that compared to the corresponding natural river, using the equivalent cross section in calculation can produce the same results of stage-discharge relationship, stage-cross sectional area relationship, dominant discharge, dominant width, and dominant depth. Our analysis on the hydraulic geometries of this river in terms of its ratio of width B to depth H demonstrates that is a function of stage, showing an overall trend of increasing from its upstream smaller to downstream larger values. All the values fall between 3.26 and 9.12 m-0.5, a value range between those of the Yangtze and the Yellow.