The invention provides a fine adjustment for a positioner. The fine adjustment comprises an upper cover plate, a lower cover plate, a positioning plate and a connector. A chamber for holding a square beam is formed between the upper cover plate and the lower cover plate. The positioning plate is used for mounting the positioner and disposed above the upper cover plate. The connector comprise a screw, a spherical pair nut and a washer; the positioning plate is adjusted to shift along an axis Z and rotate around axes X and Y by adjusting the connector; one side, facing the upper cover plate, of the positioning plate is provided with at least on wedge; the upper cover plate is provided with a cavity used for holding the wedges; the periphery of the upper cover plate is provided with at least one threaded hole communicated with the cavity; adjusting screws penetrate the threaded holes to contact the wedges; the positions of the wedges in the cavity are adjusted by adjusting the adjusting screws, and thus the positioning plate is adjusted to shift along the axes X and Y and rotate around the axis Z. The fine adjustment is simple in structure, convenient to operate and reusable.