The effect of slat angle on the daylight of office building in China has been studied. And hour-by-hour illuminance level, glare index and lighting load, with and without the use of windows with between-the-glass louvered shades, are compared. Results are presented for several slat angles(i.e,0°,±15°,±30°,±45°,±60°,±75°and ±90°) by built a typical office building model in China. Result shows that the use of windows with between-the-glass louvered shades will increase the artificial lighting load when the illuminance is not enough. However, it could avoid glare in buildings. And the result will be different when the window is used in east, west, south or north direct. A suggested slat angle control strategy is also developed under the consideration of lighting energy saving and visual comfort.