Abstract: The production flowsheet of steel P80R flat products (/% ： 0. 15C, 0.25Si, 1. 70Mn, 0. 012P, 0.002S, 3. 01 Ni, 0. 34Mo, 1. 07Cu, 1. 10AI) is 110 t LD-LF-RH-casting 4. 2 t ingot-breakdown 150 mmx615 mm slab-rolling to 60 mm x610 mm flats. It is obtained by examination and analysis that the Ni and Cu is seriously enriched near the cracks, the Ni content and Cu content in area near cracks are respectively up to 32. 55% ~ 33. 53% and 7. 97% 〜8. 86% , and the enrichment of Cu leads to surface grain boundary oxidation to form cracks, therefore the Cu content in steel, slab heating temperature and time should be controlled. By the process measures including decreasing Cu content in steel from 1.07% to 0. 92% , Al content in steel decreasing from 1. 10% to 0. 88% , increasing Ni/Cu from 2. 7 to 3. 3, reducing heating time at 1100 ~ 1140 ℃. from 30 ~50 min to 20 ~30 min and slab peeling treating, the occurrence rate of surface cracks of mirror plastic die steel P80R flats decreases from 70% to ≤0.5%.