Igneous emplacement on the NW Pacific oceanic crust via mantle activity, such as hot spots and mantle plumes, results in perturbations of crustal thickness. Therefore, mapping crustal thickness variations is key for understanding these mantle structures and processes. Improvements in resolution and accuracy of marine gravity anomalies promote the use of Moho gravity inversion effects, especially for large-scale applications. For improving the Moho gravity inversion accuracy, density variations of the lithospheric mantle are modelled via lithospheric age-temperature-density relationship since age grid with a resolution of 2 arc-minutes is available, and density variations of the mantle beneath lithosphere are modelled via seismic wave velocity-density relationship since velocity structure with penetration to 700 km is available. Comparisons between the Moho geometries by gravity inversion and seismic interpretation demonstrate that the mantle density modelling improves the Moho inversion accuracy. Our crustal map shows that (1) the crustal thickness of 26% of the NW Pacific region is thicker than 7 km; (2) the southern end of the Emperor seamounts was emplaced on the western flank of the Hess Rise, and a part of the central Hawaiian seamounts was emplaced on the eastern end of the Mid-Pacific Mountains; (3) the magma production of Hawaiian seamounts is greater than that of the Emperor seamounts; (4) the leakiness of the fracture along which the Line Islands formed decreases in the order of the central, southern and northern segments.