The utility model discloses a mechanical adjusting device for a reflecting mirror surface, and relates to the technical field of reflecting mirror surface detection. The device comprises a base, a working slideway, a sliding rail, a workbench, a sliding block, a rotating shaft, a reflecting mirror surface, an angle adjusting rod and a bevel gear set, an arc-shaped working slideway is arranged on the base; sliding rails are arranged on the two sides of the working sliding way, a groove is formed in the bottom of the workbench; the workbench is provided with a rotating shaft, the lower end of the rotating shaft is rotationally connected with the workbench, the upper end of the rotating shaft is arranged outside the workbench, the top end of the rotating shaft is connected with the reflectingmirror surface, and an angle adjusting rod is arranged on one side of the workbench and connected with the lower end of the rotating shaft through a bevel gear set. Through cooperation of the angle adjusting rod and the rotating shaft, the reflector surface can rotate around the rotation center of the reflector surface according to a fixed angle, adjustment of the swing posture of the reflector surface can be achieved through guiding movement of the workbench and the working slide way, multi-dimensional posture adjustment is achieved in a mechanical transmission mode, and cost is low.