Abstract: A one-dimensional radiation hydrodynamics numerical computation was presented for a strong explosion at sea level, of which the equivalent is 1 Mt TNT. The spatial distributions of material and radiation parameters in strong explosion, which reflect a integrate process of fireball evolution, were given in terms of the simulation. The calculation results agree well with those of some empirical formulas. The results of optical observables-radiation power versus time and fireball radius versus time were described, and the second maximum phenomenon of the fireball at low altitude was given.