Some embedding inequalities in Hardy-Sobolev space are proved. Furthermore, by the improved inequalities and the linking theorem, in a new k-order Sobolev-Hardy space, we obtain the existence of sign-changing solutions for the nonlinear elliptic equation
\left\{\begin{array}{ll}
\disp -\Delta_{(k)}u:=-\Delta
u-\frac{(N-2)^2}{4}\frac{u}{|x|^2}-\frac{1}{4}\sum\limits_{i=1}^{k-1}\frac{u}{|x|^2(\ln_{(i)}R/|x|)^2}
=f(x,u),&\quad x\in\Omega,
u=0,&\quad x\in\partial\Omega, \end{array} \right.
where 0\in \Omega \subset B_a(0)\subset {\Bbb R}^N, N\geq 3, \ln_{(i)}=\prod\limits_{j=1}^i\ln^{(j)}, and R=ae^{(k-1)}, where e^{(0)}=1, e^{(j)}=e^{e^{(j-1)}} for j\geq 1, \ln^{(1)}=\ln, \ln^{(j)}=\ln\ln^{(j-1)} for j\geq 2. Besides, positive and negative solutions are obtained by a variant mountain pass theorem.
