In view of the special importance of hydraulic steel gates in hydraulic engineerings，the limitations of traditional detection and prototype observation are analyzed，and the necessity of real-time online monitoring is proposed. Taking Minjiang Qianwei navigation-power junction real-time online monitoring as an example，the overall structure of on-line monitoring system and the cable collection and release are designed，and the monitoring and sensor selection plan of the plane fixed-wheel gate are given. The system monitors structure stress，structural dynamic response，running attitude，and fixed-wheel running state.