Abstract: The equations for one-dimensional radiation hydrodynamics in spherical symmetry were applied to the early fireball phenomenology of strong explosions with different yields. Evolutions of radiation fronts and case shocks for these early fireballs were investigated numerically and analyzed by using the scaling theory. With the increase of explosion yield, the extension velocities of radiation front and case shocks increase, the beginning and ending position and sustaining area of transition of radiation front increase, and the central temperature decrease of fireballs slows. The parameters for the fireball fronts can follow the cube-root scaling of the yield after the shock transition of the fireball fronts.