The present disclosure relates to the technical field of flat panel display, and proposes a side-lighting backlight, including a back plate on which a reflecting plate is arranged, an optical sheet assembly spaced from the back plate to form an optical cavity therebetween, and a light-emitting element arranged on one side of the back plate, wherein a convex lens is arranged between the reflecting plate and the optical sheet assembly, so that light from the light-emitting element is guided into the optical cavity through the convex lens and then exits through the optical sheet assembly, and the distance between the convex lens and the light-emitting element is greater than a light coupling distance. The convex lens can also function to keep the distance between the optical sheet assembly and the reflecting plate constant. The side-lighting backlight according to the invention has a lighter weight, a thinner thickness and a greatly simplified manufacturing process over a backlight in the prior art.