A method of controlling a braking system using a brake device having an electromechanical parking function uses a brake device having an electromechanical parking function includes: a parking release and preliminary braking step of releasing a limitation of an operation location of an electromechanical element, pressing a secondary piston by a primary piston by operating the electromechanical element, and generating a braking force in the front wheel and the rear wheel by operating a hydraulic pump that is connected to a hydraulic circuit system; a primary piston backward moving step of allowing oil inflow of an accumulator for a complex caliper unit and separating the primary piston from the secondary piston by moving the primary piston; and a primary piston forward pressing step of blocking oil inflow of an accumulator for the complex caliper unit and pressing the secondary piston by moving the primary piston by the electromechanical element.