Abstract: To address issues during the assembly process of the WS-55140 bowl head hanging plate locking pin—such as insufficient load capacity of the original DHKX-2 pin puller, low efficiency of manual pressing on ordinary punching machines, poor assembly consistency, easy deformation of workpieces, and obvious safety risks—we carried out the development and performance verification of a dedicated automated pressing tool. The study adopted a pneumatic-hydraulic boosting transmission scheme, using the STG-80-150-20-8T-50 pneumatic-hydraulic booster cylinder as the power core. After calculating load margins and checking structural strength and stiffness, we finalized the selection of the power components. We also designed precision positioning and clamping fixtures along with a linkage control system, integrating all processes including positioning and clamping, pressing and holding, and automatic resetting, forming an all-in-one automated pressing tool. The tool’s performance was verified through mechanical analysis and on-site trial assembly tests. On-site results showed that the tool’s rated pressing force can reach 80kN, with stable pressure output and a wide adjustment range. The assembly efficiency for a single workpiece increased by about 60% compared to traditional manual pressing, with product assembly qualification rates exceeding 99.5%. This effectively eliminated workpiece pressing deformation defects, reduced safety risks of manual operation, and realized lean, standardized, and safe production for high-voltage transmission fittings of this model. It can serve as an engineering reference for similar assembly processes and equipment upgrades in the power fittings industry.