The present disclosure provides a backlight module, a display device and a control method thereof, and relates to the technical field of display. The backlight module includes: a light source; an optical film; a privacy film disposed on a light exit side of the optical film, and configured to reduce a divergence angle of light from the optical film; and a dimming assembly disposed on one side of the privacy film away from the optical film, and configured to not change a divergence angle of light from the privacy film in a case of being in a first state, and increase the divergence angle of the light from the privacy film in a case of being in a second state.