The temperature data of SODA (Simple Ocean Data Assimilation) at different depths from 1815 to 2013 is used to calculate heat content in this study. EOF decomposition and power spectrum analysis are the main methods to study the three-dimensional structure and period of PDO (Pacific decadal oscillation). The results show that there are decadal oscillation characteristics in the ocean shallower than 300 m, not only at sea surface, and the most obvious decadal variability appears at subsurface about 70 m deep. The power spectrum analysis shows that the period of North Pacific decadal variability is about 18 a. Based on the temperature and salinity data of SODA, the Rossby wave phase speed in the North Pacific is calculated, and the calculation suggests that the Rossby wave is propagated westward and the phase speed declines with latitude. The lead-lag correlation between heat content time series and PDO index in the ocean shallower than 300 m indicates that when the former lags the latter by 9 a, the distribution of correlation coefficients is out-of-phase with that of the contemporaneous correlation. The evolution features of PDO are analyzed with lead-lag correlation between heat content and PDO index at different depths, the result of which shows that PDO is propagated westward through Rossby wave at low latitude and is gradually intensified during the propagation.