The key technologies necessary to develop and utilize a double-action link-type hydraulic die set for the enclosed die forging are presented in this paper. Various die sets for the enclosed die forging are investigated and the technologies necessary to develop and to utilize a double-action link-type hydraulic die set are introduced in detail with emphasis on the mechanism of the die set and its kinematical behaviors, the force transmission mechanism, the criterion on the enclosed die forging and its application, the forming load prediction and the stress distribution of the link. A double-action link-type hydraulic die set is developed and it is applied to the enclosed die forging of a bevel gear.