After thermal environments of a subway were surveyed for a year, the author developed a thermal environmental simulation program by the two- and three-dimensional finite element methods. Affluent data obtained through the survey showed theoretical values were nearly coincident with actual figures. The simulation found the outlet temperature of the tunnel rose 0.6 degree centigrade when ventilation facilities were stopped throughout the year, while it went up 1.0 degree centigrade when the heating value doubled.