This study investigated the effects of the addition of coal gasification slag (CGS) at three levels (0%, 5%, and 10% w/w) on antibiotic resistance genes (ARGs) and the bacterial community during composting. The addition of CGS effectively facilitated the removal of ARGs and mobile genetic elements (MGEs), where it significantly reduced the relative abundances of 5/11 ARGs and three MGEs in the swine manure composting product. In addition, the enrichment of ARGs and inti1 was lower under the addition of 10% CGS compared with 0% CGS. The bacterial community was distributed according to the composting time under different treatments. Redundancy analysis showed that bacterial community succession and MGE-mediated horizontal gene transfer played important roles in the variations in ARGs. Network analysis indicated the co-occurrence of ARGs and MGEs with specific microorganisms. Thus, 10% CGS may be a suitable additive for reducing the risks of ARGs in compost products.