Multiple geophysical datasets from northern Vietnam were examined and reanalyzed to explore detailed structures within the deep crust and their relationship to major tectonic fault systems in this region. Deep seismic data using explosions were collected and examined to crustal structure in northern Vietnam. Based on the determined depths of seismic boundaries, we verified crustal densities by gravity inversion model of Bouguer anomalies. Then, refer to those verified crustal densities; crustal interface boundaries along selected profiles in northern Vietnam were inverted by fitting its gravity anomalies. Integration results reveal significant lateral variations in the depth of the Moho discontinuity. The Moho depth increases from coastal to mountainous areas, and increases more rapidly towards the northwest. The rapid thickening of the crust can be considered as the southeastern extension of the eastern Tibetan along the eastern Himalayan syntaxis. We deduce that these variations are controlled by the main tectonic faults in northern Vietnam. Furthermore, although the Red River fault zone is considered as a boundary between two regional crustal blocks, however, no remarkable differences in crustal density and Moho depth were obtained by our analysis. A comparison of previous magnetotelluric studies and heat-flow observations indicates that the low resistivity of the uppermost mantle beneath the Hanoi basin region is well correlated with the location of a high heat-flow anomaly. The high heat-flow and thin crust determined in this study is suggestive of a recent rifting process of the opening of the South China Sea.