Broadband mirrors with two quarterwave stacks superimposed on the same substrat have been analysed. When the refractive indices of films are NH = 2.3 - i5×10-4 and NL=1.46-i1×10-5, two narrow absorption bands are induced in this broad band mirror. The peak value reaches 7%. The causeswhich inducing absorption band are explained in this paper and a broad band mirror with simple construction to reduce the absorption peak at the absorption band is also proposed.