A dimming mode detection circuit for an LED lighting system that receives an alternating current input voltage and generates a bus voltage to drive an LED load, the dimming mode detection circuit including: a leading edge detection circuit configured to generate a leading edge detection signal by detecting a leading edge of a first voltage representative of the bus voltage in one sine half-wave cycle, in order to determine whether the LED lighting system operates in a leading edge dimming mode; and a trailing edge detection circuit configured to generate a trailing edge detection signal in accordance with a time length of a first interval from a first value of the first voltage in a previous sine half-wave cycle to a second value of the first voltage in a next sine half-wave cycle, in order to determine whether the LED lighting system operates in a trailing edge dimming mode.