The traditional transmissive air-fed array suffers from the drawback of low power capacity and cannot be directly applied in the high-power microwave field. The existing high-power air-fed array layouts are not flexible enough and have slow beam scanning speeds, which cannot fully exploit the advantages of phased arrays in system integration. This article proposes and designs a new type of spiral radiation unit using spatial feed, and constructs a transmissive air-fed spiral array antenna. By controlling the rotation of individual spirals, two-dimensional beam scanning can be achieved, making the design more flexible and adaptable to the actual application requirements, in line with the compact and modular development trend of high-power microwave antennas. An array consisting of 324 units was simulated and designed. The numerical simulation results show that the unit S₁₁≤-20 dB, power capacity is 0.35 MW, array aperture efficiency is 0.68, and it can scan within the range of ±45°, with a maximum gain reduction of 3 dB.