A new technique for surface shape measurement is proposed, which is based on the Brox optical flow algorithm. The measurement system consists of a projector, a CCD camera and the measured object. First, one fringe pattern is projected onto a reference plane at a small angle and then two fringe images are recorded using the CCD camera before and after the measured object is added, respectively. Based on the analysis of the spatial geometry of the measurement system, the spatial relationship between the height of the object plane and the displacements of the observing point, the projector and the camera is established, in which the displacement of the observing point is obtained by estimating the optical flow distribution between two images based on the Brox optical flow algorithm. Aiming at the problem caused by the measurement system that the measurement result is not consistent with the actual shape, we analyze the cause of the error through the numerical simulation with the spherical crown geometrical model and propose a modified method. The theoretical simulation and the actual measurement verify the feasibility of the proposed method. By comparing with the Fourier transform method, it is proved that the proposed method can accurately restore the height information of the object with only two frames of images. The experimental process is simple, the measurement time is effectively shortened, and it is suitable for a dynamic measurement.