Abstract: Against the backdrop of the accelerated construction of new-type power systems, the construction of main-transformer firewalls in substations faces the dual challenges of high cost and poor adaptability of traditional steel formwork, as well as low precision and insufficient efficiency of scattered wooden formwork. Based on engineering practice, this paper proposes a flow construction process for firewalls using an integrated combined wooden formwork system. The method employs large-formwork panels made of 15 mm-thick plywood faced with square steel tube ribs, and incorporates a multi-layer force-transfer system consisting of "inner wooden ribs – outer double-steel-tube ribs – through-wall tie rods." It also integrates a zoned cross-flow construction mode and comprehensive quality control techniques, achieving synergistic optimization of the formwork system, innovative process organization, and precise quality control. Verified through the Rulin 500 kV substation and Changle 1000 kV substation projects, this method improves construction efficiency by 10%–16%, reduces total cost by 30%, and ensures first-time quality excellence compared with conventional large-steel-formwork techniques. The findings can serve as a reference for similar substation firewall construction.