An experimental roller ball milling system was established to investigate the co-grinding and co-combustion characteristics of herbal residues (HR) and lignite. The effects of HR blending ratio and moisture content on the average particle size of the mixed materials were systematically examined. Thermogravimetric analysis (TGA) was employed to study the combustion behavior of HR, lignite, and their blends with different blending ratios, and the combustion kinetic parameters were determined using the Coats-Redfern model. The results demonstrated that when the HR blending ratio was below 50wt%, the particle size of the ground materials decreased with increasing HR content. For HR blending ratios exceeding 50wt%, low-moisture HR (5%~10%) exhibited superior grindability compared to lignite, resulting in further particle size reduction. In contrast, high-moisture HR (>10%) absorbed water, leading to increased fiber flexibility and greater grinding difficulty, which consequently caused an increase in particle size. The average particle size was found to increase with moisture content, with HR showing the most significant growth rate. Field emission scanning electron microscopy observations of five mixed powder samples confirmed both the promoting and inhibiting effects during co-grinding. At HR blending ratios of 10wt% and 30wt%, lignite and HR particles showed indistinguishable morphology and excellent mixing uniformity. TGA revealed that HR possessed lower activation energy and superior burnout characteristics compared to lignite. The incorporation of HR effectively introduced an ignition source that initiated combustion at lower temperatures. The released heat elevated local temperatures of the mixed fuel, thereby reducing the ignition temperature threshold and significantly improving ignition performance. The optimal combustion efficiency was achieved at an HR blending ratio of 30wt%. However, with rising moisture content, the TG curves of mixed fuels shifted toward higher temperature regions, weakening the promoting effect of HR on lignite combustion and increasing the burnout temperature of mixed samples. This study provides theoretical guidance for the resource utilization of HR and the development of co-grinding and co-combustion technology for HR-lignite mixtures.