The present invention provides a light guide plate and a manufacturing method thereof and a side-edge backlight module using the light guide plate. The light guide plate includes a plurality of reflective separation walls arranged therein. The reflective separation walls divide the light guide plate into a plurality of sections. The reflective separation walls have surfaces forming mirror surfaces. The light guide plate includes reflective separation walls respectively arranged between independent sections to have light traveling from an independent section toward the reflective separation wall reflected back into the independent section and thus confined within the independent section. Thus, brightness sectioning and independent control of sectionalized brightness of the light guide plate can be realized and improved light isolation result can be achieved. With such a method, manufacturing a light guide plate comprising reflective separation walls is easy, has improved yield rate, is mass producible, and is of low cost.