Selecting the advanced Eddington coordinates, and adopting the statistical method ,the instantaneous radiant exitance of non_static black hole is calculated. It is found that the instantaneous radiant emittance of non_static black hole is not only related to the radiant exitance by supposing it is in the state of thermal equilibrium, but also related to the rate of change and the temperature of its event horizon, and the absorption coefficient and the radiation coefficient of the black hole. In the situation of the spherically symmetric non_static black hole, the instantaneous radiant exitance of the black hole is always proportional to quartic power of temperature of the event horizon of black holes at anytime.