Abstract: Using 9 months waveform data recorded at 44 seismic stations of Yunnan seismic network during 2008, we obtained Greenrsquo;s functions between the stations with cross-correlation analysis, and then retrieved wave dispersion curves from the Greenrsquo;s functions. Using the Greenrsquo;s functions and dispersion curves, we analyzed the sources of the regional background weak signals. The Greenrsquo;s functions show that the background weak signals in a period of 15s propagated from southeast to northwest in the Yunnan province. The azimuthal variation of the signals implies that they may be related to the effect of oceanic waves in South China Sea or southern Pacific ocean. The background signals show a seasonal variation, with the strongest signals appeared between June and September in a year. Comparing the signals with wind data, we could not find any relation between them.