310S(0Cr25Ni20) heat resistant stainless steel (typical composition % : 0.05C, 0.70Si, 0.95Mn, 0.025P, 0.006S, 24.5Cr, 19.3Ni) is a high chromium-nickel austenitic stainless steel, which has excellent corrosion resistance in oxidized media and good mechanical properties at high temperature, so it can be used for both corrosion resistant parts and high temperature parts. When the steel mill produces 310S heat-resistant stainless steel, the continuous casting process is easy to produce the defect of the longitudinal crack of the billet. Most of the longitudinal crack is concentrated in the middle of the inner arc side of the billet, which is serrated and unequal in length. Technical personnel have carried on the analysis, found that 310S austenitic heat resistant stainless steel (% : 0.05C, 24.5Cr, 19.3Ni) have poor thermal conductivity [100℃ thermal conductivity 0.029× 4.18j /(cm•℃)], and 200mm×(950-2150)mm continuous casting slab is prone to longitudinal cracks (width 0.1 ~ 10mm, depth 1 ~ 20mm). By using the slag with melting point of 1085℃ (ST-SP/310) instead of the slag with melting point of 1120℃ (ST-SP/810), the cooling water flow rates of the wide and narrow sides of the mold are reduced from 4500L/min and 460L/min to 4300L/min and 430L/min, respectively. The superheat of molten steel decreases from 30 ~ 45℃ to 20 ~ 35℃, and the drawing speed decreases from 0.95/m/min to 0.80 ~ 0.90m/min.