The present invention discloses a multi-stage DC-DC converter, a power supply device and a display device, wherein the multi-stage DC-DC converter is connected with a power supply converter and a backlight light source and comprises N stages of voltage conversion modules connected in series, and N is greater than or equal to 2; a direct current voltage output by the power supply converter is received by a first-stage voltage conversion module and is then converted into a first voltage which is output to a second-level voltage conversion module; the first voltage is subjected to voltage conversion via the second-level voltage conversion module and then a second voltage is output; the rest can be done in the same manner; After each voltage conversion module is controlled to perform voltage conversion, an Nth voltage conversion module outputs a preset power supply voltage to the backlight light source. Through step-by-step voltage conversion, output voltage of the DC-DC converter can be flexibly adjusted to meet requirements of voltage specifications of different backlight sources, compatibility of power supply devices can be improved, and production test efficiency of display module groups can be effectively improved.