It analyzes the application of flat style in web interface design. It explores the core issues about the flat style in web design， through the applicsation of graphical abstract method， removing image background， emotional color oriented method，color levels collocation and specific fonts in the flat style web design. Starting from improving the user experience， using the design philosophy that is "the less is more"， a reasonable relationship among the graphics， color and words is integrated to achieve the aesthetic and function of the interface design. Designers should reasonably treat the flat design style， catch the essence of its design， rather than the blind pursuit of new design trends.