A combined steam-gas plant with in-cycle steam gasification of coal and hot gas purification is considered as a promising technology for increasing the efficiency of energy production with simultaneous reduction in environmental impact. To intensify steam-air gasification, mechanical activation of fuel is used; it consists in high-stress grinding in a mill-disintegrator. The supply of steam to the gasifier allows an increase in reactivity of fuel, suppression of sorbent decomposition in the unit of hot desulfurization, reduction in the steam load on the shift reactor, increase in useful external work of gas turbine expansion, reduction in nitrogen oxide formation, and general increase in the efficiency and ecological compatibility of energy generation. On the other hand, a significant amount of steam can deteriorate the heat balance and efficiency of the gasifier. In this work, the influence of the steam/fuel ratio on steam-air gasification of mechanically activated Kuznetsk coal in a flow reactor was studied experimentally. The excess air coefficient was maintained constant and equal to 0.51, which corresponded to a temperature at the reactor outlet of about 1100°C. When steam was supplied, the fuel and air-flow rates were adjusted to ensure a constant gas-dynamic regime. To evaluate the obtained regimes, the heat and material balances were compiled. A positive effect of steam on characteristics of the gasification process was revealed. For the studied coal, the maximum degree of coal conversion and the calorific value of synthesis gas are achieved with a steam/fuel ratio of about 0.4 kg/kg.