For the super large flange forgings with Φ7.3 m for 09MnNiD low temperature steel produced by forging for the first time, through analysis and comparison of three kinds of forming schemes, including tailor welding after segment bending, ring rolling and free forging and reaming, and the scheme of free forging and reaming was determined. In order to eliminate the influences of widening amount of reaming and cold shrinkage rate of hot forgings during the forging process on the sizes of finished flange forgings, through the analysis on the widening amount of reaming and the cold shrinkage rate of hot forgings during the forging process of super large ring, the parameter setting basis for the widening amount of reaming in the forging process design was determined, and the reference data for the cold shrinkage rate of hot forgings were statistically analyzed. In view of the problem that the wall thickness of flange forgings for 09MnNiD low temperature steel exceeded 400 mm, which resulted in poor heat treatment hardening effect and high risk of unqualified performance, the heat treatment process test was systematically carried out, and according to the results of heat treatment process test, the best heat treatment process scheme of 09MnNiD low temperature steel was determined. The actual production shows that the rationality of the widening amount of reaming, the cold shrinkage rate of hot forgings and the heat treatment process parameters in the forging process design for super large ring of 09MnNiD low temperature steel is verified.