Abstract: This study addresses issues such as suboptimal product quality and combustion control difficulties encountered during underground coal gasification by employing non-focused microwave technology to pre-treat coal pillars, thereby enhancing gasification efficiency. With Zhangminggou bituminous coal as the research subject, an underground gasification experimental system for non-focused microwave-modified coal bodies′ is established. The investigation systematically examined the impact of varying microwave parameters on the efficiency, cleanliness, and safety of underground coal gasification. Experimental results demonstrate that non-focused microwave radiation effectively improves coal gasification performance. Under optimized modification parameters, the average syngas content is increased from 42.39% to 44.67%, while the effective gas production time is extended from 0.90 h to 1.00 h. Meanwhile, minimal impact is exerted on tar concentration. Furthermore, analysis of the syngas explosion risk revealed that the duration within the explosive limits increased following modification. This indirectly indicates a more sustained and stable gasification process alongside improved product quality. This research provides experimental evidence for optimizing the underground gasification process through non-focused microwave modification, thereby enhancing product quality.