We demonstrate by using Wiedemann's gluon radiative spectrum that heavy quark radiative energy loss spectrum can be factorized as the light quark radiative energy loss spectrum times a dead cone factor in the absence of medium effect. The availability of factorial approach with a dead cone approximation in medium is studied by Djordjevic-Gyulassy (D-G) and GLV (M.Gyulassy, P.Levai and I.Vitev) formulas. The numerical results show that the factorial method with a dead cone approximation is more suitable for c...