Abstract: In the current practical system, due to the existence of noise, the full-field phase value cannot be obtained when the single-frequency grating is phase-resolved point by point, which leads to the low reconstruction accuracy of small objects with complex profiles. A multi-frequency grating projection method was proposed to realize the high-precision reconstruction of the objects with small volume and complex morphology. The system algorithm decomposed the multi-frequency grating based on the improved four-step phase-shifting method which changed with time series. The multi-frequency grating decomposition separately expanded the phase of each frequency grating, and the grating decomposition of each frequency was carried out point by point. The discontinuous phase in the single-frequency grating due to noise could be repaired by fitting other frequency gratings, and a continuous phase in the whole field could be obtained. Experimental results show that the error range of single-frequency structured light is 0.1 mm～0.5 mm for measuring small and complex objects, while the precision of our method is 0.03 mm～0.05 mm, which can be improved by about 10 times.