Metal-organic framework derivatives have emerged as promising contenders for microwave absorption, with their morphology considerably influencing their electromagnetic wave absorption capabilities. However, owing to the uncontrollability of precise derivative structures, challenges persist in improving reflection loss (RL) and absorption bandwidth. Herein, we proposed a “capping agent induction” strategy using cetyltrimethylammonium bromide as a surfactant to precisely control the size and morphology of zeolite imidazolate framework (ZIF)-8 crystals, followed by pyrolysis in air. We demonstrated the process of capping agent-induced crystal growth toward multiple dimensions and revealed the regulation of microwave absorption. As a result, the optimized carbon-based magnetic material (ZnO-N-C) exhibited a minimum RL of −47.64 dB at 4.32 GHz with a thickness of 2 mm, along with an effective absorption bandwidth of 3.82 GHz. We achieved an effective absorption bandwidth of 6.8 GHz at a thickness of 2.5 mm, reflecting the effectiveness of our application design.