Based on existed problems in small batch production of the big gear ring forgings, such as the high cost of die forging process and the large machining allowance of the primary ring free forging process, the traditional reaming technology was studied and improved by core shaft. Under the premise of ensuring the strength, the traditional circular section core shaft was replaced with 60° fan-shaped cross-section core shaft, which made the external dimension of core shaft to be reduced greatly. The advantages of reaming technology are simple, practical,convenient and more flexible. The free-forging process of similar shaped forgings was realized to produce the big gear ring forgings in small batch.