A backlight, an assembly method thereof and a display device are disclosed. The backlight includes a light source configured to emit light having a first wavelength; a wavelength converter disposed on a light-emitting side of the light source and configured to convert the light having the first wavelength into light having a second wavelength upon passing through the wavelength converter, in which the second wavelength is different from the first wavelength; and a light guide plate disposed on one side of the wavelength converter away from the light source, and configured to receive and re-emit the light emitted from the wavelength converter.