Navigation drop-down menu is a common effect in browsing web pages, and it is an important content in the frontend development of WEB. Using DIV + CSS, we can make navigation drop-down menu with rich effect. In this paper, DIV is used for navigation layout. The drop-down menu of horizontal navigation consists of UL unordered list and CSS. In the process of realizing the effect of navigation drop-down submenu, the method of setting the CSS style of each page element is given, and the specific application method of each CSS style attribute is analyzed.