Abstract: Gas drainage wells are special channels for extracting coal mine gas to the surface, and their construction safety is critically important. With the deepening of coal mining, the diameter and weight of casings in gas drainage wells have increased, making the traditional suspension method unable to meet the safety requirements of casing running. The buoyancy casing technique has become a key solution, yet it suffers from the potential hazard of relative sliding between the cement buoyancy plug and the casing wall. To address this issue, micro-expansion concrete was proposed for preparing buoyancy plugs to enhance the bonding strength between buoyancy plugs and the casing wall. Nine groups of mix proportions of micro-expansion concrete were designed, and the effects of water-cement ratio, expansion agent content, water reducer content, and fly ash content on the bonding strength between the cement buoyancy plug and the casing wall were systematically investigated through orthogonal experiments. The maximum pressure, the slope from the initial position to the maximum pressure, the slope from the maximum pressure to 20 mm displacement, and the pressure at 40 mm displacement obtained from the pressure-displacement curves were selected as evaluation indexes to quantitatively characterize the bonding performance of micro-expansion cement buoyancy plug specimens. Based on range analysis, factor-index trend charts, and influence weight tables, the optimal mix proportion of high-performance micro-expansion concrete with balanced bonding properties was determined. The results show that the optimal mass ratio is cement: water: sand: gravel: expansion agent: water reducer: fly ash = 1.000∶0.250∶1.360∶3.030∶0.100∶0.008∶0.150.