Drilling gas-drainage holes in soft coal seams is essential for preventing coal and gas explosions. After analyzing and summarizing the advantages and disadvantages of existing spiral drilling and wind-pressure drilling processes, a new technology of drilling in soft coal seams using a foam drilling fluid is proposed in this paper. Experiments were conducted to determine the optimal drilling fluid formula for drilling to depths greater than 200 m. The most effective foam stabilizers are selected and correlations of foam half-life and volume with stabilizer concentration were found. Based on an analysis and comparison of all drilling fluid formulas, the recommended additives are 5% K-12 + 0.6% Sesbania powder + 1.0% Konjac powder or 5% K-12 + 0.8% Sesbania powder + 1.0% HEC. In field tests, five holes deeper than 200 m were drilled successfully by using this formula.