A method and device for measuring dimension of a semiconductor structure are provided. A probe of an Atomic Force Microscope (AFM) is controlled at first to move a first distance from a preset reference position to a top surface of a semiconductor structure to be measured in a direction perpendicular to the top surface of the semiconductor structure to be measured, then the probe is controlled to scan the surface of the semiconductor structure to be measured while keeping the first distance in a direction parallel to the top surface of the semiconductor structure to be measured, amplitudes of the probe at respective scanning points on the surface of the semiconductor structure to be measured are detected, and a Critical Dimension (CD) of the semiconductor structure to be measured is determined according to the amplitudes of the probe at respective scanning points on the surface of the semiconductor structure.