The North Pacific meridional overturning circulation (NPMOC) is the general name given to the five North Pacific overturning cells: the subtropical cell (STC), the tropical cell (TC), the subpolar cell (SPC), the deep tropical cell (DTC), and the thermocline cell (THC). These cells are important for the leakage of meridional material and energy exchange. The NPMOC and its variation play an important role in the upper ocean thermohaline structure and climate change. The structure of the STC, TC, and DTC, and the level and mechanism of variation in these are currently being extensively analyzed, and a preliminary analysis of poleward heat transport by the STC has been completed. Less research has been undertaken on the SPC and THC; however, the three-dimensional structure and mechanism of variation remains unknown. In addition, research into heat and salt transport by the NPMOC is still at an initial stage, with little knowledge at present about the characteristics and the level and mechanism of variation within each cell. Therefore, this requires further investigation in the future.