Steam mining method was injecting hot steam into the borehole to heat the hydrate strata at the same time of depressurization mining，which could promote further decomposition and expand mining areas of gas hydrate． Steam heat calculation would provide the basis for the design of heating device and the choice of the field test parameters． There were piping heat loss in the process of mining． The heat transfer of steam flowing in the pipe was steady，so the heat loss could be obtained easily by formula calculation． The power of stratum heating should be determined by numerical simulation for the process of heating was dynamic and the equations were usually nonlinear． The selected mining conditions were 500-millimeter mining radius，10 centigrade mining temperature and 180 centigrade steam temperature． Heat loss and best heating power，obtained by formula calculation and numerical simulation，were 21． 35 W/m and 20 kW．