Based on the relative position relationship between the measured object and the high-frequency fringe in the on-line three-dimensional (3D) measurement, an improved dual-frequency on-line 3D measurement method is proposed. By controlling the acquisition points when the measured object moves, the light intensity distribution of the high-frequency fringe in each deformed pattern after pixel matching can be exactly consistent. The full-cycle equal phase-shift algorithm is directly applied for phase calculation so that the filtering process is avoided and the 3D reconstruction accuracy is improved. The light intensity component of the high-frequency fringe is designed to be much smaller than that of the low-frequency fringe, and it can be considered as faint background light and the interference of high-frequency fringe on phase calculation is further reduced. The simulated and experimental results show that compared with other methods, the proposed method can improve the reconstruction accuracy effectively.