The invention relates to an integrated double-main-cylinder line control braking system. The system comprises an ECU electronic control unit, an electronic pedal, a pedal displacement sensor, a first braking passage, a second braking passage and a braking liquid loop. Double-main-cylinder design is adopted in the system, an assisting main cylinder, namely the second main cylinder is additionally arranged, pressure is applied through a motor and a lead screw instead of a plunger pump and an energy accumulator originally, a working cavity and a liquid supplementing cavity of the second main cylinder can be switched freely, the motor does not need to rotate forwards and reversely frequently, the service life of the motor is prolonged, and braking response time is shortened. Meanwhile, multiple braking manners can be provided through the system, especially in the micro-braking process, the assisting main cylinder does not work, a conventional main cylinder applies pressure, the working time of the motor is shortened, and the service life of the motor is prolonged.