Using entropy density of scalar field near event horizon in an arbitrarily accelerating black hole with electric charge and magnetic charge, we study the law for the thermal radiation of black hole and the instantaneous radiation energy flux is obtained. It is found that the thermal radiation of a black hole always satisfies the generalized Stefan-Boltzmann’s law. The proportional coefficient of generalized Stefan-Boltzmann is no longer a constant, and it becomes a dynamic coefficient that is related to the parameters of the black hole. For different dynamic black holes, the obtained generalized Stefan-Boltzmann’s dynamic proportional coefficient is different from each other, because the gravitation field and electromagnetic field around black holes is not the same.