Observations indicated that in the region of the Subtropical Countercurrent (STCC) over the Pacific (140°E-170°W, 19°N-28°N), the eddy kinetic energy over the western side is much higher than that over the eastern side. The cause of such a behavior was theoretically investigated in this paper. The calculation of geostrophic current in this region indicates that there are relatively strong meridional geostrophic currents in this region even though the zonal current is dominant in most seasons. Using a 2.5-layer reduced-gravity model, baroclinic instability of non-zonal current was discussed. It is found that at the western side of STCC the vertical shear of the meridional geostrophic current will be in favor of the baroclinic instability, but at its eastern side it will suppress baroclinic instability, thus causing the growth of eddies over the western side much faster than that over the eastern side. Observations indicate that in the region of the Subtropical Countercurrent (STCC) over the Pacific (140 ° E-170 ° W, 19 ° N-28 ° N), the eddy kinetic energy over the western side is much higher than that over the eastern The cause of such a behavior was theoretically investigated in this paper. The calculation of geostrophic current in this region indicates that there are more strong meridional geostrophic currents in dominant than most seasons. Using a 2.5- it is found that at the western side of STCC the vertical shear of the meridional geostrophic current will be be in favor of the baroclinic instability but but at its eastern side it will suppress baroclinic instability, thus causing the growth of eddies over the western side much faster than that over the eastern side.