Abstract: To adapt to the design of a green and low-carbon power grid, a 40.5 kV/1250 A environmentally friendly gas-insulated switchgear isolation gas box based on cylindrical copper busbars was designed, and its feasibility was analyzed through simulation. The safe dimensions of the copper busbars were determined through current-carrying capacity calculation and withstand voltage tests, and resistance and electric field simulation analyses were conducted using simulation software. The results show that a method for calculating the resistance of complex-shaped conductors using electromagnetic simulation was proposed. Under the simulation of the power frequency withstand voltage electric field, the insulation design and arrangement of the cylindrical copper busbars and the bushings inside the box meet the insulation requirements. This paper provides a new selection and basis for the design of the circuit copper busbars of 40.5 kV/1250 A environmentally friendly gas-insulated switchgear.