The South China Sea (SCS) has experienced complex thermal and dynamic evolution, with the loading of numerous seamounts in the central basin. To explore the controlling factors of lithospheric strength and their relationship with seamount evolution in SCS, we first calculate the density distribution of the crust using the ParkerOldenburg method and then apply it to estimate the spatial variations of effective elastic thickness of the lithosphere (Te) with the ‘fan’ wavelet admittance method. Te in oceanic lithosphere is relatively low and mainly distributed in the range of 0~16 km. Te is correlated positively with curiepoint depth and negatively with surface heat flow, indicating a strong influence of geotherm on Te. However, Te of the seamounts show no correction with the time of loading, indicating strong magmatism and thermal anomalies weakened the lithosphere around seamounts.