The invention relates to an electronic mechanical drive-by-wire brake. The electronic mechanical drive-by-wire brake comprises a motor, a transmission mechanism, a one-way clutch, a gear, a rack, a piston, a friction limiting device and the like. The one-way clutch is driven to rotate by the motor through the transmission mechanism, and the gear is driven to rotate by the one-way clutch; the piston and a caliper body are driven to move in the opposite direction by a gear and rack mechanism, and friction plates are tightly pressed by same forces from both sides of a brake disc, so that the efficient braking effect is achieved. The electronic mechanical drive-by-wire brake is simple in structure, reliable in operation, high in braking efficiency, braking clearance can be adjusted automatically, influence caused by abrasion of the friction plates can be compensated, design for a controlling system is simplified, and the electronic mechanical drive-by-wire brake can be used for the service braking and parking brake.