The invention relates to a stress uniformizing method for a high-temperature alloy casing ring forging. The circumference lengths L1 and L2 at the maximum ring diameter position and the minimum ring diameter position of the high-temperature alloy casing ring forging are measured, the yield stress sigma and required strain epsilon of high-temperature alloy are obtained through a material tensile test, and a bulging mold is manufactured according to the cross section shape and size of the high-temperature alloy casing ring forging; the high-temperature alloy casing ring forging is heated to be lower than the forging temperature and is placed in the bulging mold after soaking, a bulging cone head operates downwards by H1 and then returns after being kept for a period of time, the high-temperature alloy casing ring forging is rotated by a certain angle around the axis of the ring forging, and the bulging cone head operates downwards by H2 on the basis of H1 and is kept for a period of time, so that it is guaranteed that all positions of the high-temperature alloy casing ring forging are in the state of micro plastic deformation; and finally, the bulging cone head returns, and the high-temperature alloy casing ring forging is taken out and air-cooled to the room temperature. Uniform circumferential plastic strain is applied to the high-temperature alloy casing ring forging through the minimum deformation so as to adjust uniform distribution of residual stress.