Abstract The North-Central coasts of Vietnam are vulnerable due to the effects of global warming and sea level rise. With quite mildly sloping foreshore, these low-lying coasts have been modelled in a non-hydrostatic and phase solving SWASH to investigate the spectral wave period at nearshore and then compare the empirical equation proposed by Hofland et al., 2017. Especially, the ratio of the predicted spectral wave period at shore to deep water was overestimated in comparison with the previous research, reaching up to 1.9 for the milder slope. Furthermore, a simulation of wave energy spectra measured in Altomare et al., 2016 was also considered in this research. A well-matched result can be seen in both physical observations and modeling calculations. A comparison was further investigated for a mild seabed with a rising sea level. Notably, the significant wave height at nearshore increases by approximately 1.4 times when sea levels rise, even while the wave characteristics at the offshore boundary remain the same.