The utility model discloses a B-type reverse-flow type ball screw pair. The B-type reverse-flow type ball screw pair comprises a lead screw, a nut and backflow devices. Each backflow device is provided with an arc guide groove, wherein one end of the arc guide groove is provided with a semi-annular eccentric flange; the two sides of the other end of the arc guide groove are respectively provided with a wedge-shaped clamping-blocking structure; a tongue-shaped guide sheet is arranged between the bottoms of the clamping-blocking structures; the eccentric flange is connected with one end of a corresponding reverse channel through a backflow device mounting hole in the reverse channel; the guide sheet between the clamping-blocking structures is connected with ball inlets or ball outlets in the two ends of each rolling path. The B-type reverse-flow type ball screw pair is simple in structure, the backflow devices and the reverse channels are long in service life and not prone to being damaged, the axial size is large, the number of steel balls, used for bearing loads, in the rolling paths is increased under the same length of the nut, and then the bearing capacity of the ball screw pair is greatly enhanced.