This study uses monthly sea surface temperature (SST) data from the ERSSTv5 dataset, along with 10-m wind, 10-m wind speed, sea level pressure (SLP), latent heat flux, 2-m air temperature, and 2-m dew point data from the ERA5 reanalysis during 1955-2024. The Pacific Meridional Mode (PMM) is defined via maximum covariance analysis. Using a combination of statistical methods including the decomposition of Wind-Evaporation-SST (WES) feedback and regression analysis, we investigate the long-term trends of PMM and explore potential mechanisms driving its variations from the perspectives of atmospheric variability and subtropical feedback. The results reveal a significant intensification of PMM since 1990, with a strengthening trend also evident during spring. The enhancement of PMM is attributed to the synergistic effects of mid-to-high-latitude atmospheric variability and subtropical feedback. On the one hand, the North Pacific Oscillation (NPO) exhibits a strengthened influence on PMM, where winter SLP anomalies enhance the sensitivity of subtropical North Pacific SST to atmospheric forcing by modulating latent heat flux and surface wind fields. Notably, NPO-related spring SST anomalies in the subtropical North Pacific show a high correlation with spring PMM intensity over the study period. On the other hand, the WES feedback intensity in the subtropical North Pacific has significantly strengthened since 1990, further amplifying PMM-associated SST anomalies. This enhancement primarily stems from the combined effects of sustained background SST warming and reduced relative humidity in the subtropical North Pacific.