Abstract: An objectve regionalization of SST field in Northern Pacific is set up using the orthogonally rotated factor analysis based on maximum variance criterion. The result shows that the whole Northern Pacific SST field may be divided into five regions: (1) the equatorial eastern Pacific region; (2) the north trade wind region off California; (3) the western Pacific region; (4) the northern Pacific region; (5) the central Pacific region. It is obvious that the regions correspond well with ocean currents and spatial distribution of thermal flux for the whole nortern Pacific. In particular, Region (1) is stable and has the maximum weight in the whole SST field for Northern Pacific and contributes most to it by being secularly stable. Furthermore,from the power and cross spectra of the SST time series,significant periods in inter-monthly SST oscillations for individual regions and marked coupling ones among them are derived. Characteristic of time-frequency correlation , all dominant oscillations are associated with Region (1) .