In order to improve the ability of recognizing the details of the measured free-form surface, restrain the jumping error caused by the processing of phase unwrapping, and reduce the sufficient conditions for the correct phase unwrapping, a full-frequency phase unwrapping algorithm based on multi-frequency heterodyne is proposed. First, the standard four-step phase shifting algorithm is used to solve the wrapped phase. Then, using the full-frequency phase unwrapping algorithm, the details contained in the fringe pattern with different pitches are converted by the relationship between the phase and the fringe pitch to improve the accuracy of the unwrapped phase details. Compared with the existing method, less constraints are derived in order to restrain the jumping error caused by the processing of phase unwrapping. Simulation results show that the proposed method has no jumping error after the phase unwrapping, and no additional error correction is needed. Experimental results verify that the three-dimensional reconstruction has higher precision, the reconstructed surface is smoother and the details are clearer. Compared with the existing method, the standard deviation of phase unwrapped error of the proposed method is reduced by 44%.