The invention relates to a flocculant mixing device. An adding spray pipe, a first-level mixing prick (4), a grid plate (5), a second-level mixing prick (6) and a mixing ring (7) are concentrically mounted in turn along the flow direction in a pipe (3). The entry end (1) of the adding spray pipe is communicated with the adding device and the nozzle (2) of the adding spray pipe is set in the center of the pipe (3) and over against the top of the first-level mixing prick (4) and a discharge hole (9) is set on a tower seat plate (8) of the first-level mixing prick (4); the top of the second-level mixing prick (6) is toward the grid plate (5), and the bottom of the second-level mixing prick (6) is oppositely fixed on the mixing ring (7) of the inner wall of the pipe (3) and the shape and mount direction of the second-level mixing prick (6) are same to that of the first-level mixing prick (4). The flocculant mixing device completely realizes the mixing of the flocculant in a solid-liquid two-phase flow by the pulp self-flowing energy to improve the pulp sinking performance and quicken the sinking speed. Therefore the flocculant mixing device has features of simple structure, convenient use, uniform mixing of the flocculant in the solid-liquid two-phase flow and quick mixing speed.