  We study the radiative leptonic decays of heavy mesons within the covariant
light-front model. Using this model, both the form factors F_V and F_A have the
same form when the heavy quark limit is taken. In addition, the relation
between the form factor F_V and the decay constant of heavy meson F_H is
obtained. The hadronic parameter \beta can be determine by the parameters
appearing in the wave function of heavy meson. We find that the value of \beta
is not only quite smaller than the one in the non-relativistic case, but also
insensitive to the value of light quark mass m_q. These results mean that the
relativistic effects are very important in this work. We also obtain the
branching ratio of B\to l\nu_l \gamma is about (1.40-1.67)\times 10^{-6}, in
agreement with the general estimates in the literature.
