  This paper is concerned with the weak solution for the fast diffusion
equation with absorption and singularity in the form of $u_t=\triangle u^m
-u^p$. We first prove the existence and decay estimate of weak solution when
the fast diffusion index satisfies $0<m<1$ and the absorption index is $p>1$.
Then we show the asymptotic convergence of weak solution to the corresponding
Barenblatt solution for $\frac{n-1}{n}<m<1$ and $p>m+\frac{2}{n}$ via the
entropy dissipation method combining the generalized Shannon's inequality and
Csisz$\mathrm{\acute{a}}$r-Kullback inequality. The singularity of spatial
diffusion causes us the technical challenges for the asymptotic behavior of
weak solution.
