An LED dimming circuit, wherein the LED dimming circuit comprises: a low-level-voltage generation module, configured to perform a low-level counting operation comprising counting cycles of a high-frequency clock signal during a low level duration of a low-frequency PWM signal in order to measure the low level duration, and to convert the low level duration to obtain a low-level voltage, wherein the low-level voltage has a value corresponding to the low level duration; a high-level-voltage generation module, configured to perform high-level counting operation comprising counting cycles of the high-frequency clock signal during a high level duration of the low-frequency PWM signal in order to measure the high level duration, and to convert the high level duration to obtain a high-level voltage, wherein the high-level voltage has a value corresponding to the high level duration; a base-voltage generation module, connected to an output of the low-level-voltage generation module and to an output of the high-level-voltage generation module, wherein the base-voltage generation module is configured to charge a third capacitor by a constant current to result in a terminal voltage of the third capacitor, to obtain a high-frequency switching signal based on comparison between the terminal voltage of the third capacitor and the high-level voltage, and to control a period of the high-frequency switching signal based on comparison between the terminal voltage of the third capacitor and the sum of the low-level voltage and the high-level voltage; and, under the control of the high-frequency switching signal, to charge and discharge a fourth capacitor based on a reference voltage to generate a base voltage, wherein the base voltage is related to the low-frequency PWM signal only in terms of a duty cycle of the low-frequency PWM signal; a dimming-signal generation module, connected to an output of the base-voltage generation module, wherein the dimming-signal generation module is configured to output the base voltage as a dimming signal when the base voltage is greater than a predetermined voltage, and to output a new PWM signal as the dimming signal when the base voltage is less than the predetermined voltage, wherein the new PWM signal has a magnitude equal to that of the predetermined voltage and a frequency independent of the low-frequency PWM signal, wherein the new PWM signal has an average value equal to that of the base voltage. a low-level-voltage generation module, configured to perform a low-level counting operation comprising counting cycles of a high-frequency clock signal during a low level duration of a low-frequency PWM signal in order to measure the low level duration, and to convert the low level duration to obtain a low-level voltage, wherein the low-level voltage has a value corresponding to the low level duration; a high-level-voltage generation module, configured to perform high-level counting operation comprising counting cycles of the high-frequency clock signal during a high level duration of the low-frequency PWM signal in order to measure the high level duration, and to convert the high level duration to obtain a high-level voltage, wherein the high-level voltage has a value corresponding to the high level duration; a base-voltage generation module, connected to an output of the low-level-voltage generation module and to an output of the high-level-voltage generation module, wherein the base-voltage generation module is configured to charge a third capacitor by a constant current to result in a terminal voltage of the third capacitor, to obtain a high-frequency switching signal based on comparison between the terminal voltage of the third capacitor and the high-level voltage, and to control a period of the high-frequency switching signal based on comparison between the terminal voltage of the third capacitor and the sum of the low-level voltage and the high-level voltage; and, under the control of the high-frequency switching signal, to charge and discharge a fourth capacitor based on a reference voltage to generate a base voltage, wherein the base voltage is related to the low-frequency PWM signal only in terms of a duty cycle of the low-frequency PWM signal; a dimming-signal generation module, connected to an output of the base-voltage generation module, wherein the dimming-signal generation module is configured to output the base voltage as a dimming signal when the base voltage is greater than a predetermined voltage, and to output a new PWM signal as the dimming signal when the base voltage is less than the predetermined voltage, wherein the new PWM signal has a magnitude equal to that of the predetermined voltage and a frequency independent of the low-frequency PWM signal, wherein the new PWM signal has an average value equal to that of the base voltage.