The invention discloses a wafer stress measuring method, and belongs to the technical field of a semiconductor device. The method comprises the following steps: step 1, measuring a light spot offset amount along an X direction after each incident light beam along the X direction is reflected by a wafer, rotating a sample pallet, enabling the wafer to rotate, and measuring the light spot offset amount of each incident point along a Y direction when each incident light beam scans along the Y direction on the wafer; step 2, through the light spot offset amount of each incident light beam along the X direction, calculating the curvature radius of the wafer along the X direction, and through the light spot offset amount of each incident point along the Y direction, calculating the curvature radius of the wafer along the Y direction; and step 3, according to a formula (1) shown in descriptions, calculating stress. By applying the measuring apparatus and the measuring method provided by the invention, the wafer stress in the wafer X direction and the wafer Y direction can be simultaneously measured.