A method for producing a steel for a main shaft bearing of a wind turbine, comprising the following steps: smelting of molten steel, wherein raw materials are sequentially treated by KR pretreatment of molten iron, smelting by electric furnace or converter, LF refining, and RH or VD vacuum degassing; continuous casting of CCM large continuous casting billet with large cross-section; wherein the continuous casting billet meets the following requirements: C: 0.10~0.30%, Si: 0.10~0.50%, Mn: 0.30 ~ 0.80%, Cr: 1.30 ~ 1.60%, S≤0.025%, P≤0.025%, Ni: 3.25 ~ 3.75%, Cu≤0.30%, Mo: 0.15 ~ 0.25%, Al: 0.005-0.05%, N: 0.005 -0.015%, Ca≤0.0010%, Ti≤0.003%, O≤0.0015%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, the balance is Fe and unavoidable impurities; slow cooling of continuous casting billet, followed by softening annealing, wherein the slow cooling of continuous casting billet is performing the slow cooling in a pit, wherein a temperature of the billet entering the pit is greater than 600°C, and the duration of the slow cooling in the pit is greater than 48 hours, a temperature of the billet exiting the pit is less than 200°C, and the softening annealing is carried out within 24 hours after the billet is removed out of the pit, the softening annealing temperature is 600-700°C, the time of heating and holding the temperature is ≥10h, and then the billets are cooled to 450°C with the furnace, and then air-cooled to the room temperature after being removed out of the furnace; continuous rolling: after heating to 1150°C-1280°C in a heating furnace with a neutral atmosphere, and the time of heating and holding the temperature is ≥7h, the continuous casting billet out of the furnace is dephosphorized by high pressure water and then rolled into round bars in rough rolling - medium rolling - finishing rolling machines, with the total compression ratio of ≥ 4, and the rough rolling temperature is 1000-1150°C; after that, the austenite grains heated at high temperature are recrystallized and refined, and the final rolling temperature is controlled at 800-950°C to make the final rolling performed in the non-recrystallization temperature range, which lengthens the deformed austenite grains; as there are many deformation bands in the grains, the ferrite grains after phase transformation can be refined; slow cooling and softening annealing, wherein the rolled bars having a temperature of 480°C or above are slowly cooled in a pit, wherein the slow cooling lasts more than 60 hours, a temperature of the bars exiting the pit is less than 200°C, and the bars are subjected to softening annealing within 24 hours after being removed out of the pit, the softening annealing temperature is 600-700°C, the holding time is ≥7h, and then the material is cooled to 500°C in the furnace, and then air-cooled to the room temperature after being removed out of the furnace; finishing. smelting of molten steel, wherein raw materials are sequentially treated by KR pretreatment of molten iron, smelting by electric furnace or converter, LF refining, and RH or VD vacuum degassing; continuous casting of CCM large continuous casting billet with large cross-section; wherein the continuous casting billet meets the following requirements: C: 0.10~0.30%, Si: 0.10~0.50%, Mn: 0.30 ~ 0.80%, Cr: 1.30 ~ 1.60%, S≤0.025%, P≤0.025%, Ni: 3.25 ~ 3.75%, Cu≤0.30%, Mo: 0.15 ~ 0.25%, Al: 0.005-0.05%, N: 0.005 -0.015%, Ca≤0.0010%, Ti≤0.003%, O≤0.0015%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, the balance is Fe and unavoidable impurities; slow cooling of continuous casting billet, followed by softening annealing, wherein the slow cooling of continuous casting billet is performing the slow cooling in a pit, wherein a temperature of the billet entering the pit is greater than 600°C, and the duration of the slow cooling in the pit is greater than 48 hours, a temperature of the billet exiting the pit is less than 200°C, and the softening annealing is carried out within 24 hours after the billet is removed out of the pit, the softening annealing temperature is 600-700°C, the time of heating and holding the temperature is ≥10h, and then the billets are cooled to 450°C with the furnace, and then air-cooled to the room temperature after being removed out of the furnace; continuous rolling: after heating to 1150°C-1280°C in a heating furnace with a neutral atmosphere, and the time of heating and holding the temperature is ≥7h, the continuous casting billet out of the furnace is dephosphorized by high pressure water and then rolled into round bars in rough rolling - medium rolling - finishing rolling machines, with the total compression ratio of ≥ 4, and the rough rolling temperature is 1000-1150°C; after that, the austenite grains heated at high temperature are recrystallized and refined, and the final rolling temperature is controlled at 800-950°C to make the final rolling performed in the non-recrystallization temperature range, which lengthens the deformed austenite grains; as there are many deformation bands in the grains, the ferrite grains after phase transformation can be refined; slow cooling and softening annealing, wherein the rolled bars having a temperature of 480°C or above are slowly cooled in a pit, wherein the slow cooling lasts more than 60 hours, a temperature of the bars exiting the pit is less than 200°C, and the bars are subjected to softening annealing within 24 hours after being removed out of the pit, the softening annealing temperature is 600-700°C, the holding time is ≥7h, and then the material is cooled to 500°C in the furnace, and then air-cooled to the room temperature after being removed out of the furnace; finishing.