Abstract: The mathematical relationship between heat dissipation from a intravehi cular space suit and air ventilating parameters(air temperature,air flow rate and relative humidity) as well as metabolic state(at rest or exercise) of man is founded by calculating the data from 24 tests performed on 6 young male subjects wearing space suit at sea level.Combined second design is employed to arrange the tests.The thermal characteristics of the suit and their influences are figured out according to the mathematical model.