  In this paper, we study the initial and boundary value problem of the
Navier-Stokes equations in the half space. We prove the unique existence of
weak solution $u\in L^q(\R_+\times (0,T))$ with $\nabla u\in
L^{\frac{q}{2}}_{loc}(\R_+\times (0,T))$ for a short time interval when the
initial data $h\in {B}_q^{-\frac{2}{q}}(\R_+)$ and the boundary data $ g\in
L^q(0,T;B^{-\frac{1}{q}}_q(\Rn))+L^q(\Rn;B^{-\frac{1}{2q}}_q(0,T)) $ with
normal component $g_n\in L^q(0,T;\dot{B}^{-\frac{1}{q}}_q(\Rn))$,
$n+2<q<\infty$ are given.
