The present invention discloses a frequency-modulated dimming control system of a discharge lamp. The frequency-modulated dimming control system of a discharge lamp includes including a voltage regulator having a variable output voltage for converting an input voltage into a bus voltage, wherein a level of the bus voltage is a predetermined ratio of the input voltage, for example 10% of the input voltage, and a ballast circuit for driving the discharge lamp by detecting a variation of the bus voltage and then providing a current to the discharge lamp in response to a frequency modulation of the ballast circuit and the variation of the bus voltage so as to control a light intensity of the discharge lamp.