The spectral nudging (SP) method is used in simulating continuous precipitation processes that occurred over South China in early 2008. The results show that the spatial distribution and intensity of precipitation in the SP experiment is obviously better than that without use of this method (NOSP). For the area affected frequently by troughs or wind shear lines in lower layers, a 2-4-day oscillation period of meridional wind is found in the SP experiment, which is consistent with observations. This means that the SP method may enhance the simulation ability of the meridional wind field. Based on a comprehensive analysis of the water vapor transport pathway, the model domains and periodicity features of high-correlation regions in advance of the water vapor channel, we find that the SP method can introduce meridional vapor transport information over the eastern Indo-China Peninsula into the model, improving the simulation ability of the cycle of the water vapor budget in the precipitation area. This could be an important reason why the SP method improves the rainfall simulation in the SP experiment. Furthermore, the variables indirectly affected by the SP method are statistically improved by means of the interaction with other variables in the SP experiment. Above all, the exogenous cycle characteristic factors introduced by the SP method, which adjust the coordination between modeling and large-scale forcing fields, could improve simulation results within a forecast time of two weeks. This method has the potential to be of practical value in numerical prediction.