The invention discloses a machining method for effectively improving quality of a large forging, belongs to the technical field of smelting and forging, and belongs to an improvement on the smelting and forging of the large forging. The method comprises the steps of firstly, in the smelting process, prefabricating a water gap jaw in the water gap end of an ingot, so the distribution state of water gap deposition cones is changed and the metallurgical quality of the ingot is improved; secondly, adopting riser-free forging in the forging loop and changing the fiber direction of the forging, so the forging quality of the ingot water gap is effectively improved. Through the improvement on the smelting and forging, the hot-working quality of the large forging is effectively improved.