An online cooling device for Hbeam was built with mist cooling instead of air cooling which is effective for cooling Rpart at a speed of more than 100 ℃/s. The results showed that, the surface quality of beams was improved, the microstructure was refined, and the yield strength and tensile strength were both increased by more than 21 MPa and the mechanical properties were uniform. The temperature of workpiece before cooling bed was lower to match doubled the productivity.