Based on the analysis of the existing methods of on-line discharge monitoring of hydrometry stations, this paper summarizes the latest research progress of velocity-area method and hydraulic method in on-line discharge monitoring. Cross section discharge was calculated based on local flow velocity, and the on-line discharge monitoring method based on velocity-area method is divided into three categories: index-velocity method, velocity distribution model method and surface velocity method. This paper analyzes the advantages and disadvantages of H-ADCP method, V-ADCP method, two-line energy slope method, radar method, particle image method, water measuring building method and hydraulic building method, and points out that further research will be carried out in improving online discharge monitoring accuracy, improving stability and promoting application.