Abstract: The detection of dark matter remains a paramount scientific objective in modern astronomy and physics. Axions from Quantum Chromodynamics (QCD) have emerged as natural candidates for dark matter due to their theoretical properties. Currently, efforts are focused on detecting axions with micro-electronvolt mass using electromagnetic responses in GHz-band microwave cavities, but these experiments have yielded null results. Therefore, it is imperative to explore detection strategies for lower-mass axions. This paper addresses the need for detecting lighter axions with sub-electronvolt mass by discussing the design and optimization of tunable microwave cavities in the hundreds of MHz band. The study explores the optimal resonant modes, shape factors, and frequency scanning rates for these cavities. Numerical simulations indicate that the proposed eight-rod cavity structure increases the scanning rate nearly a hundredfold compared to standard cavities in the same frequency band, with a reduction in axion detection sensitivity by only about threefold. Although the results presented are based on numerical simulations and require experimental validation, this research offers a forward-looking reference for constructing future experimental setups for QCD axion electromagnetic response detection in the sub-GHz frequency band.