The invention provides a flame cutting system with an insulation device for a flame cutting zone of billets, which comprises track beams arranged on both sides. The top parts of the track beams are respectively provided with a heavy track, a flame cutting trolley slides back and forth on the heavy tracks, the front end and the rear end of the flame cutting trolley are respectively connected with at least one mobile insulation cover, the mobile insulation covers are connected with each other and slide back and forth on the heavy tracks along with the flame cutting trolley, a row of internal water cooling billet-conveying rollers with an insulation device are arranged between the two track beams, billet cantilever rollers penetrate through the internal water cooling billet-conveying rollers, and billets arranged below the flame cutting trolley slide back and forth on the billet cantilever rollers. The invention has the advantages of minimizing the heat dissipation of the billets, preventing the air leakage of the joint surface, effectively solving the problem of sealing the shaft end, efficiently preventing heat dissipation, ensuring the performance and strength of the roller rings,and reducing the consumption of cooling water.