  In this paper, we investigate three symmetry breaking effects in strong and
radiative decays of strange heavy mesons. We study 1/m_Q corrections within the
heavy quark effect theory, as well as SU(3) and SU(2) symmetry breakings
induced by light quark mass differences and the \eta-\pi mixing vertex. These
effects are studied in a covariant model. The numerical results show that the
1/m_Q corrections of the coupling constants are consistent with \alpha_s
\Lambda_{QCD}/m_Q. The SU(3) symmetry violating effect of the strong coupling
constant is obviously larger than that of the magnetic coupling constant. The
value of the \eta-\pi mixing vertex has some changes because of the renewed
data. As compared with the other theoretical calculations and the experimental
data, our radiative decay rates are much larger than those of the other
theoretical methods, except for \chiPT; however, our branching ratios are close
to the experimental data.
