Disclosed is a hydraulic control apparatus of a brake system including a modulator block having a motor bore, and a motor including a cover that covers an opening of a case accommodating a stator and a rotor and is supported on one side of the modulator block, wherein a vent hole for air flow between the inside and the outside of the motor is formed on the cover and a communication passage for communicating the motor bore and the vent hole is formed in the modulator block.