The present invention discloses a light emitting device control circuit with dimming function and a control method thereof. The light emitting device control circuit includes: a dimmer circuit, a rectifier and filter circuit, a power converter circuit, and a headroom voltage regulation circuit. The dimmer circuit generates an AC dimming voltage according to an AC voltage. The rectifier and filter circuit generates an input voltage according to the AC dimming voltage. The power converter circuit operates according to a control signal to convert the input voltage to an output voltage which is supplied to a light emitting device circuit. The headroom voltage regulation circuit generates the control signal according to a reference value and a difference between the input voltage and the output voltage, and regulates the difference at a level corresponding to the reference value by a feedback control loop.