  The upper and lower critical field, and the critical field ratio of an
anisotropic two-band magnetic superconductors in Ginzburg-Landau(GL) scenery is
derived analytically. The temperature-dependent on the upper critical field is
investigated and applied to Fe-based superconductors. We find that the very
high value of zero-temperature upper critical field in Fe-based superconductors
can be found in the negative differential susceptibility region. The
temperature-dependent upper critical field is presented in two formulas as in
the empirical view and in the GL two-band view that agrees with the experiment
results.
