Abstract: In this study, complex empirical orthogonal function (CEOF) analysis was applied to 73 years of stratospheric wind field data for July from the National Center for Atmospheric Research and National Centers for Environmental Prediction reanalysis project, covering 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 examined. The results show that the first three modes accounted for 60.9%, 24.0%, and 4.4% of the total variance, respectively, with the first two modes cumulatively explaining 84.9%. These two modes effectively captured the principal features of the QBO. Above the 50 hPa pressure level, the wind anomalies in the first and second modes were dominated by partial latitudinal winds, however, the first mode exhibited vertically consistent wind directions, while the second showed opposite wind directions. The time coefficients of the two modes exhibited interannual variations of 2.25 and 2.47 years, respectively. The former aligned with the average QBO period, while the latter fell within the typical QBO range of 1.75–2.5 years. The interdecadal variations of both modes were not significant. In terms of the intensity variation of wind anomalies, both modes exhibited interannual variations of about 8 years, and the decadal variations in both were not significant. The typical values of wind anomalies in both modes rapidly decreased below 50 hPa and were very small at 100hPa, consistent with QBO characteristics. The maximum anomalies in the two modes were located at 20 and 10 hPa, respectively, with the former closely matching the peak altitude of the QBO. 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, a linear intensification trend was observed in the strength of the wind field in the latter, which had accelerated since 2010. This trend might be related to the remarkable global warming. The physical properties of the first and second modes corresponded to barotropic and baroclinic Kelvin waves, respectively. This indicated that Kelvin waves play a key role in QBO formation, with the barotropic component contributing more prominently.