Abstract: The present invention provides a luminance auto-adjustment device for the display, which comprises a light source-detecting module and a voltage modulation module, which are set in the power control circuit of the rear-projection fluorescent tube of the display. The light source-detecting module is used to sense the external luminance, based on which the voltage modulation module is used to modulate the voltage value of the rear-projection fluorescent tube. The rear-projection fluorescent tube of the display can automatically modulate the luminance according to the external luminance.