Abstract: The effect of electroslag remelting(ESR) on nonmetallic inclusions in an optimal component 42 CrMo steel was studied by BX51 M optical microscopy and Image Pro-Plus software,and the continuous cooling transformation(CCT) curve was measured on a Gleeble3000 thermal simulation machine. These results show that ESR can reduce the number and size of inclusions in steel samples and the inclusions removal ratio reaches 71.90%. The CCT curve of 42 CrMo steel was plotted according to the thermal expansion curve and microstructure. When the cooling rate is lower,the microstructure is ferrite,pearlite and bainite; but when the cooling rate is higher,there are martensite and a small amount of bainite.