  We consider a priori estimates of Weyl's embedding problem of $(\mathbb{S}^2,
g)$ in general $3$-dimensional Riemannian manifold $(N^3, \bar g)$. We
establish interior $C^2$ estimate under natural geometric assumption. Together
with a recent work by Li and Wang, we obtain an isometric embedding of
$(\mathbb{S}^2,g)$ in Riemannian manifold. In addition, we reprove Weyl's
embedding theorem in space form under the condition that $g\in C^2$ with $D^2g$
Dini continuous.
