This paper conducts an in-depth research into the energy exchange and fundamental law of thermal equilibrium radiation, with the classic statistic theory as its tool. The energy exchange between vibrators and the radiation field is made up of two levels of stimulation and absorption. This paper for the first time discovers the law of how vibrators stimulate and absorb radiation, by a study of the black-body radiation law, the Planck formula and the characteristics of vibrators' absorption of radiation. As for the fundamental law of thermal equilibrium radiation, we've managed to give the following complete statement: the energy distribution of vibrators in the thermal equilibrium radiation field follows the energy distribution law by L. Boltzmann; the probability of vibrators' stimulating radiation is directly proportional to their energy state and that of their absorbing radiation is directly proportional to their energy distribution. The former reveals the law of energy distribution of vibrators from a static state and the latter reveals the law of energy exchange between vibrators and the radiation field from a dynamic state, which are generally called the fundamental law of thermal radiation.
Thermal Equilibrium Radiation, State of Energy Levels, Probability of Energy Levels, Energy Exchange, Fundamental Law of Thermal Radiation.