  We study the hadronic form factors of $\tau$ lepton decays $\tau \to K
\pi(\eta) \nu$. We compute one loop corrections to the form factors using the
chiral Lagrangian including vector mesons. The counterterms which subtract the
divergence of the one-loop amplitudes are determined by using background field
method. In the vector form factor, $K^\ast$ resonance behavior is reproduced
because the diagram with a vector meson propagator is included. We fit the data
of the hadronic invariant mass spectrum measured by Belle by determining some
of the counterterms of the Lagrangian. Besides the hadronic invariant mass
spectrum, the forward-backward asymmetry is predicted. We also study the effect
of CP violation of a two Higgs doublet model. In the model, CP violation of the
neutral Higgs sector generates the mixing of CP even Higgs and CP odd Higgs. We
show how the mixing leads to the direct CP violation of the $\tau$ decays and
predict the CP violation of the forward-backward asymmetry.
