  Let $\Gamma$ be a Lipschitz curve on the complex plane $\mathbb{C}$ and
$\Omega_+$ is the domain above $\Gamma$, we define Hardy space $H^p(\Omega_+)$
as the set of holomorphic functions $F$ satisfying $\sup_{\tau>0}(\int_{\Gamma}
|F(\zeta+\mathrm{i}\tau)|^p |\,\mathrm{d}\zeta|)^{\frac1p}< \infty$. We mainly
focus on the case of $1<p<\infty$ in this paper, and prove that if $F(w)\in
H^p(\Omega_+)$, then $F(w)$ has non-tangential boundary limit $F(\zeta)$ a.e.
on $\Gamma$, and $F(w)$ is the Cauchy integral of $F(\zeta)$. We denote the
conformal mapping from $\mathbb{C}_+$ onto $\Omega_+$ as $\Phi$, and then prove
that, $ H^p(\Omega_+)$ is isomorphic to $H^p(\mathbb{C}_+)$, the classical
Hardy space on upper half plane, under the mapping $T\colon F\to
F(\Phi(z))\cdot (\Phi'(z))^\frac{1}{p}$, where $F\in H^p(\Omega_+)$.
