The invention discloses a main lifting parallel operation height balance correcting system of two 400-ton bridge cranes, comprising master controllers of two overhead traveling cranes, a main hook winch drum and a main hook motor, wherein each overhead traveling crane also comprises a cab substation, a communication master station, a trolley communication substation, a main hook frequency converter, an absolute value encoder and an incremental encoder; the main hook motor is a main hook variable frequency motor; the output end of the main hook variable frequency motor is provided with the incremental code, the output end of which is connected with the main hook frequency converter; the main hook variable frequency motor is also connected with the main hook frequency converter; the absolute value encoder is installed on the main hook winch drum and connected with the trolley communication substation; the trolley communication substation is connected with the communication master station; the communication master station is connected with the cab substation; the cab substation is connected with the master controllers; the main hook frequency converter is connected with the communication master station; and the two communication master stations of the two overhead traveling cranes are connected. The invention realizes that the two cranes keep at the same height all the time and ensures the degree of balance of the two overhead traveling cranes hoisting rotors and the safety of the hoist of a generator.