  In this work we study the radiative leptonic decays of $B^-$, $D^-$ and
$D_s^-\to \gamma l \bar{\nu}$, including both the short-distance and
long-distance contributions. The short-distance contribution is calculated by
using the relativistic quark model, where the bound state wave function we used
is that obtained in the relativistic potential model. The long-distance
contribution is estimated by using vector meson dominance model.
