The results of this paper extend the existed results of normal systems to descriptor systems . 8 . lower and upper matrix bounds for the positive semidefinite solution of discrete - time riccati matrix equation are obtained 给出离散ricoati方程和统一的耦合代数ricoati方程的半正定解的上、下矩阵边界估计,并得到求离散ricoat方程和统一的耦合代数ricoati方程的半正定解的两个迭代算法。