A backlight source comprising a light source, guide fibers and transmission fibers, the guide fibers and the transmission fibers are coupled by means of a coupling joint, wherein the first end of the guide fiber is coupled to the light source, the second end of the guide fiber is flexibly coupled to the first port of the coupling joint, and/or the first end of the transmission fiber is flexibly coupled to the second port of the coupling joint, and the second end of the transmission fiber is provided with a reflection head; the light emitted from the light source passes through the guide fiber and enters into the coupling joint, then is transmitted into the transmission fiber, and is finally emitted by the reflection head. The backlight source is collapsible and is thus flexible and convenient to use. Embodiments of the present disclosure also provide a transparent display device.