The peak reflectivity,bandwidth and centroid wavelength of Extreme Ultraviolet Lithography (EUVL) Mask as a function of roughness,period thickness and thickness ratio of Mo/Si multilayers were calculated. Nine equations were obtained by fitting the calculated data. Then,the reflective spectrum of 6 mirror EUVL system were simulated,and calculation were performed to work out the relative illumination intensity at wafer plane. Finally,illumination uniformity error at wafer plane induced by the mask were analyzed,and resulted a formula for estimating the error.