In order to solve the inherent problems of high upsetting pressure and difficulty in filling corners for precision forgings of pie-shaped cylindrical gear formed in one-step by conventional flashless die forging, the recently proposed enlarged-corner cavity die forming by changing the shape of die cavity was emphatically introduced based on the reasonable composition of two-step/multi-step forming processes, such as integrated opened forming, divided flow forming and push-through shaping. The forming method enlarged the space of bottom corner and adjacent area of die which is difficult to fill, so that more metal flowed to the adjacent corner and occupied part of the expanding space in the upsetting stage. Then, the intermediate workpiece with sufficient volume of bottom corner and less regular shape was acquired, and the local constraints on the deformed metal were relieved by the inclined enlarged-corner side wall and the upsetting pressure was decreased. When the corner with sufficient volume and less regular shape was ejected, the metal flowing into the expanded-corner space flowed to the bottom corner to complete the filling of bottom corner due to the action of inclined side wall. The test results of cylindrical gears and cylindrical internal gears show that the upsetting pressure drops by more than 50% while ensuring that the corners are full. Thus, the seemingly contradictory problems of dropping the upsetting pressure and improving the corner filling can be solved in coordination through the enlarged-corner cavity die forming under the condition of conventional equipment.