Abstract: In this study, complex empirical orthogonal function (CEOF) analysis was applied to the 73-year stratospheric wind fields in July of NCAR/NCEP at pressure levels of 10, 20, 30, 50, 70, and 100 hPa over the equatorial Pacific. The relationship between the diagnostic results and the Quasi Biennial Oscillation（QBO）was discussed. The main conclusions were as follows: The variance contributions of the first three modes were 60.9%, 24.0% and 4.4%, respectively. The cumulative variance contribution of the first two modes was 84.9%, which could basically summarize the nature and characteristics of QBO. The obvious wind anomalies of the first and second modes above 50hPa were dominated by the partial latitudinal winds. The difference was that the former exhibited vertically consistent wind direction, while the latter was opposite wind direction. The time coefficients of the two modes had inter-annual variations of 2.25 and 2.47 years, respectively. The former period had the same period as the average period of QBO, while the latter period located within the period range of 1.75-2.5 years of QBO. The inter-decadal variations of both modes were not significant. In terms of the intensity variation of wind anomalies, both had an inter-annual variation of about 8 years, and the decadal variations of both were also not significant. The typical values of wind anomalies in both modes decreased rapidly below 50 hPa and were very small at 100 hPa, which is quite consistent with the situation of QBO. The maximum anomalies of the two modes were located at 20 and 10 hPa, respectively, with the former closely matching the QBO’s peak altitude. The most obvious QBO intensity variations of the two modes initiated from 1995 and 1990, respectively, and continued until the end of 2020. In addition, there was a linear intensification trend in the strength of the wind field in the latter, which had accelerated since 2010. It might be related to the significant global warming. The physical properties of the first and second modes corresponded to barotropic and baroclinic Kelvin waves, respectively. This indicated that the Kelvin wave was crucial for the formation of QBO and was one of the important factors for the generation of QBO. Notably, barotropic Kelvin wave contributed more prominently to the QBO.