Considering that the N-step phase shift method cannot overcome the nonlinear response of the projection equipment in the measurement system, and in order to suppress the jumping error of the three-frequency heterodyne phase unwrapping, we proposed a 3D measurement method based on double-N-step phase shift and full-frequency phase unwrapping.Firstly, the initial and fused wrapped phases are solved by standard double-4-step phase shift method, and the combined wrapped phases are determined according to the fringe modulation system.Then the first-order fringe series is obtained by using the three-frequency heterodyne method, and the unwrapped phase of the second-order fringe is obtained based on the relationship between fringe series and phase in the full-frequency phase-unwrapping algorithm.The experimental results show that the proposed method is simple in implementation, smooth in phase expansion and has no jumping error.Compared with the existing methods, the proposed method has better phase unwrapping effect.