Abstract: Characteristics of the tropical intra-seasonal oscillation are analyzed using three kinds of data (NCEP/NCAR reanalysis data, NCEP/DOE reanalysis data and ECMWF/ERA40 reanalysis data) in three climate states of 1961—1991, 1971—2000 and 1981—2010. There is a significant 30—60 d oscillation period of 200 hPa zonal wind in different climate states of different reanalysis data. Different intra-seasonal oscillation characteristics can be found in different data and in different climate states. It is found that in 1981—2010 climate state compared with the other two climate states (1971—2000 and 1981—2010), annual cycle characteristics of the tropical intra-seasonal oscillation are more pronounced, strong in winter-spring and weak in summer-autumn. The tropical intra-seasonal oscillation is stronger in the tropical Indian Ocean and the tropical western Pacific Ocean, also its active areas extend eastwards and become larger. The eastward propagating energy of the tropical intra-seasonal oscillation centers more in 1—3 waves, while the westward propagating energy becomes weaker. The tropical intra-seasonal oscillation starts northward propagating later. It propagates southward strongly which spreads to the Southern Hemisphere in the beginning of May. NCEP/NCAR reanalysis data and NCEP/DOE reanalysis data match well in the annual cycle characteristics of tropical intra-seasonal oscillation, intensity and energy propagation. While NCEP/NCAR reanalysis data and ERA40 reanalysis data have some distinctions: The tropical intra-seasonal oscillation periods center in 20—100 d and its peak value is 55 d of NCEP/NCAR reanalysis data, while its oscillation periods are 20—60 d and its peak value is 50 d of ERA40 reanalysis data. As to the periods of 80—100 d, the oscillation pattern of ERA40 reanalysis data is stronger than that of NCEP/DOE reanalysis data. The tropical intra-seasonal oscillation variance contribution proportion of NCEP/NCAR reanalysis data is a little less than that of ERA40 reanalysis data in the tropical Indian Ocean and the tropical western Pacific Ocean, while stronger than that of ERA40 reanalysis data in the Eastern Equatorial Pacific Ocean. From December to the middle of March, the tropical intra-seasonal oscillation intensity of ECMWF data is stronger than that of NCEP/NCAR reanalysis data. While from the middle of March to November, the tropical intra-seasonal oscillation intensity of ERA40 reanalysis data is weaker than that of NCEP/NCAR reanalysis data; the tropical intra-seasonal oscillation phase of ERA40 reanalysis data is about 10 days ahead of NCEP/NCAR reanalysis data. The eastward propagating energy of the tropical intra-seasonal oscillation of NCEP/NCAR reanalysis data is weaker than that of ERA40 reanalysis data, while the westward propagating energy is stronger than that of ERA40 reanalysis data. In the middle of July, the northward propagating of NCEP/NCAR data is weaker than that of ERA40 reanalysis data.