The present invention relates to the technical field of display, and discloses a method for obtaining and processing backlight brightness data, and a liquid crystal display device. The method comprises: receiving a PWM dimming signal sent by a PWM controller (201); determining whether the received PWM dimming signal comprises preset hopping or not (202); if the PWM dimming signal comprises the preset hopping, sending a reading instruction to an optical sensor unit within the set time after the preset hopping (203); and receiving backlight brightness data obtained by the optical sensor unit according to the reading instruction (204). The solution achieves the purpose of improving the stability of the backlight brightness data.