To meet the wide angular bandpass requirement of a small-size mirror in extreme ultra violet (EUV) lithography illumination system, the designed broadband molybdenum (Mo) /silicon (Si) multilayer stack is deposited by using the relationship between effective thickness of Si layers and velocity and the relationship between periodic thickness of multilayers and velocity. Mo/Si periodic multilayers with different periodic thicknesses and G (ratio of Mo layer thickness and periodic thickness of multilayer films) are deposited by magnetron sputtering and characterized by small-angle X-ray reflectometry. The relationship between periodic thickness of multilayers and velocity, the relationship between effective thickness of Mo and Si layers and velocity, and the interface roughness of multilayers are provided by characterization of X-ray reflection spectrum. The broadband multilayer stack is designed by utilizing the Levenberg-Marquardt algorithm, and the designed EUV reflectance is R=42%±1% at the range of 16.8°~24.8°. The designed stack is deposited according to the relationship between effective thickness of Si layers and velocity and the relationship between periodic thickness of multilayers and velocity. The measured EUV reflectance of the broadband Mo/Si multilayer stack is 41.2%~43.0% at the range of 16.8°~24.8°, which is very close to the designed value. Further fabrication error reversion indicates that the small difference between the experimental and designed results is mainly caused by the systematic error in the calibration of G value and interface roughness of Mo/Si multilayers.