Abstract: In this paper, numerical computation about relative dependence of planar single layer chiral medium on its electromagnetic characteristic parameter ε,μ,ζ and chiral coated-layer's thickness d is presented. According to the computed result shows that chiral parameter ζ may not always improve absorption of chiral coated layer. The normal chiral parameter ζr=1 if absorption is the best in the situation which chiral parameter improves the absorption of chiral coated-layer. It is concluded that the reflectance may decrease to some constant when the thickness increases to some limited value. Of course, the electromagnetic characteristic parameters change, the limited thickness change too. Permittivity and permeability also affect the reflectance of the chiral coated-layer.