The roles of wind stress and surface heat flux in generating the Pacific interannual and interdecadal variability are examined by using two sets of simulations performed with LASG/IAP climate ocean model named LICOM. It is found that the interannual variability of SST in the tropical Pacific is mainly controlled by wind stress, however, the simulation of El Niño is improved significantly when surface heat flux is considered. The interannual variability of SST in the North Pacific is generated by the effect of surface heat flux, though it can be reproduced partly in a simulation without interannual variability of surface heat flux. Simulation without interdecadal variability of surface heat flux fails to reproduce the Pacific Decadal Oscillation (PDO) pattern, which confirms that the interdecadal variability of SST is governed by surface heat flux. To reveal the contributions of surface flux, horizontal advection, vertical advection and diffusion (including horizontal and vertical diffusion) to the variability of winter averaged upper ocean temperature in different areas, the upper ocean heat budget is examined by using the output of LICOM_HW run. It shows that SST is controlled by different mechanisms in different regions. The anomaly of temperature trend is determined by both net surface heat flux and horizontal advection in the central North Pacific. But in the coast off California, only the anomaly of net surface heat flux is found to be dominant. In the Kuroshio and Kuroshio Extension (KKE) region, the contributions of net surface heat flux and the oceanic nonlinearity effect are significant, but the contributions of horizontal advection and diffusion should not be neglected.