The invention provides a backlight module and a liquid crystal display device. Only a first supporting mechanism and a second supporting mechanism are adopted in the backlight module to support a corresponding display panel, and then a U-type back plate is used for fixing a guide plate, a reflector plate, an optical membrane set and other components in the backlight module. Compared with the prior art, as two side edge supporting mechanisms are omitted, it is avoided that the two corresponding side edges of the backlight module are made wide to arrange the supporting mechanisms, then the border width of a liquid crystal displayer adopting the backlight module is reduced, the borders of the liquid crystal displayer can be made narrow, the requirement for the border width of clients are met, user experience is promoted, and cost is reduced.