A constant-current LED driving circuit comprising an output voltage adjustable circuit and a plurality of LED loads, (311, 312, 31n), wherein each LED load comprises one or more LEDs (LED 11, LED mn) and a current-limiting circuit (321, 322, 32n) connected in series with the one or more LEDs (LED11, LEDmn) the current-limiting circuit (321, 322, 32n) is adapted to limit a maximum current in the one or more LEDs (LED11, LEDmn) the plurality of LED loads are connected with the output voltage adjustable circuit via two terminals, and the plurality of LED loads are independent from each other; wherein the output voltage adjustable circuit comprises: a switch conversion main circuit for connecting a power supply and outputting an adjustable voltage to the plurality of LED loads; and an output characteristic parameter sampling circuit for sampling an output characteristic parameter of the switch conversion main circuit and outputting a sampled signal of the output characteristic parameter; characterized in that: the output voltage adjustable circuit comprises an output voltage controller for adjusting an output voltage of the switch conversion main circuit according to a variation relationship between the sampled signal and the output voltage, wherein adjusting the output voltage of the switch conversion main circuit comprises determining a direction for adjusting the output voltage of the switch conversion main circuit according to the variation relationship between the sampled signal and the output voltage and adjusting the output voltage of the switch conversion main circuit at a preset step, so that finally the output voltage is equal to a voltage of LEDs in one LED load whose LEDs have the highest voltage or the output voltage has a difference within a predetermined range as compared to the voltage of the LEDs in the LED load whose LEDs have the highest voltage. a switch conversion main circuit for connecting a power supply and outputting an adjustable voltage to the plurality of LED loads; and an output characteristic parameter sampling circuit for sampling an output characteristic parameter of the switch conversion main circuit and outputting a sampled signal of the output characteristic parameter; characterized in that: the output voltage adjustable circuit comprises an output voltage controller for adjusting an output voltage of the switch conversion main circuit according to a variation relationship between the sampled signal and the output voltage, wherein adjusting the output voltage of the switch conversion main circuit comprises determining a direction for adjusting the output voltage of the switch conversion main circuit according to the variation relationship between the sampled signal and the output voltage and adjusting the output voltage of the switch conversion main circuit at a preset step, so that finally the output voltage is equal to a voltage of LEDs in one LED load whose LEDs have the highest voltage or the output voltage has a difference within a predetermined range as compared to the voltage of the LEDs in the LED load whose LEDs have the highest voltage. the output voltage adjustable circuit comprises an output voltage controller for adjusting an output voltage of the switch conversion main circuit according to a variation relationship between the sampled signal and the output voltage, wherein adjusting the output voltage of the switch conversion main circuit comprises determining a direction for adjusting the output voltage of the switch conversion main circuit according to the variation relationship between the sampled signal and the output voltage and adjusting the output voltage of the switch conversion main circuit at a preset step, so that finally the output voltage is equal to a voltage of LEDs in one LED load whose LEDs have the highest voltage or the output voltage has a difference within a predetermined range as compared to the voltage of the LEDs in the LED load whose LEDs have the highest voltage.