Abstract: Objective: Highspeed railway usually adopts constant tension rail cars for power supply overhead line installation. The research is specificallt carried out to tackle the track resource usage conflict between constant tension overhead contact line installation and construction unit, and the problem of overhead line installation occupying the steel rails laid in place prestation by the construction unit.Method: Based on the mechanical principles of the existing track constant tension OLI equipment and in combination with the actual highspeed railway construction site situation, a new type of vehicle set for highspeed railway trackless constant tension OLI is jointly developed with the manufacturer. The vehicle set is mainly composed of three parts: tension machine, traction machine, and hydraulic payoff rack. The hydraulic tension machine has a tension of 040 kN (single reel) or 080 kN (double reel) for each group of payoff reels, and the maximum payoff speed is 5 km/h, which can achieve stepless speed regulation; the rated traction force of the hydraulic traction machine is 35 kN, and the corresponding traction speed is 2.5 km/h, the maximum OLI speed is 5 km/h with a corresponding traction force of 20 kN.Result & Conclusion: The performance indicators of this new type OLI vehicle set meet the highspeed overhead line constant tension installation requirements; through the development of this highspeed railway trackless constant tension installation device, laid rails are no longer needed for OLI, thus the constraints on rail laying progress at station front is eliminated for construction units, and competition for station front rail occupation time and resource becomes irrelevant, greatly alleviating the problem of delayed OLI work progress in case of tight construction periods. During joint commissioning and test, the various inspection data of the anchor section installed by trackless constant tension OLI equipment meet the acceptance standards, and dynamic test shows good equipment status after launching.