The invention relates to a brake-by-wire device with a redundancy function and a control method thereof. The device comprises a brake disc, calipers, a power take-off gear, a gear shaft, a lead screwshaft, an electromagnetic clutch, a nut assembly, a return motor, a motor support, a support, a brake oil cylinder, a right friction plate, a left friction plate, a first two-position two-way electromagnetic valve, a second two-position two-way electromagnetic valve, a vehicle speed sensor, a controller and a gear sensor. Vehicle kinetic energy can be fully utilized as a power source, a driving motor adopted in the prior art is omitted, and the cost is effectively reduced; a gear power take-off mechanism is used for driving an execution structure to generate braking force, and the braking force of a brake is controlled through the electromagnetic clutch. A redundancy function is realized through coupling with a conventional hydraulic braking system; the brake-by-wire device has the advantages of the high integration level, the high response speed and low cost; and when a vehicle is braked and locked, a hydraulic braking switch control mode is changed into a braking force continuous adjustable mode, and higher control precision is achieved.