Abstract: By analyzing microstructure and inclusions, analyzing chemical composition and mechanical properties of 4J36 alloy (/% ：0. 17 ~0.18C,0. 18 〜0.27Si,0.39 〜0. 40Mn,0.009P, < 0.0005S,35. 8 〜36.ONi) before and after ESR(electro-slag remelting) , the effect of ESR on microstructure and mechanical properties of 4J36 alloy is studied. The results show that after ESR the chemical composition of 4J36 has almost no change, the sizes of gains decrease, and the amount and sizes of inclusions also decrease. Yield strength and tensile strength are improved to a certain extent, elongation increases from original 34% to 58% , and impact energy at - 196℃. increases from original 145 J to 208 J.