  We use the Dirac equation to study the mass spectrum of mesons with
heavy-light quark combinations. First we study the Dirac equation with
spherically symmetry and funnel potential, and apply them on the hydrogen-like
atom problem to check the correctness of our numerical program. Then we test
the parameters in Olsson's paper. We show that Olsson's parameters are good in
fitting the averaged central mass, but fail to get correct energy fine
splitting. Finally we fit the mass spectrum data of D, D_s, B and B_s mesons
with our parameters by solve the Dirac equation and funnel potential, calculate
the energy splitting of the S and P states. Our parameters can fit the mass and
fine splitting with errors in less than 7 MeV.
