The online inspection instrument for catenary parameters is a portable measurement system for catenary geometric parameters. The system uses image recognition, visual measurement and data fusion technology to realize the automatic and intelligent detection of catenary, and then completes the online high-precision measurement of key geometric parameters of catenary. In the process of implementation, the system can realize on-line measurement of catenary height, pull-out value, track gauge and outer rail superelevation parameters, which not only greatly improves the efficiency of daily inspection of catenary, but also greatly reduces the labor intensity of personnel.