The effective elastic thickness (Te) of the lithosphere reflects the long-term flexural strength and provides mechanical information about the evolution and deformation of the lithosphere. The Chinese mainland and its surroundings (CMS) comprise sharply contrasting tectonic domains and involve a complex evolution history. In this paper, we apply a joint inversion of real admittance and coherence calculated using the continuous planar wavelet transform to estimate the spatial variations of Te in the CMS based on topography and Bouguer gravity anomaly data. A probabilistic Bayesian inference method is used to show the statistical distribution of the model parameters in specific cases, demonstrating the accuracy and stability of the joint inversion. Old stable cratons and basins (e.g., Indian Plate, Tarim Basin, Junggar Basin and Lower Yangtze) mostly correspond to high Te (>50 km), whereas reactivated Mongolian Plateau, eastern North China Craton, Cathaysian Block, continental margins and young oceanic lithospheres tend to display low Te (<25 km). Moreover, Te correlates remarkably well with lithospheric thermal structure; areas with high Te are mostly characterized by low heat flow and large Curie-point depth, and vice versa. We conclude that the geothermal state plays an important role in controlling the continental lithospheric strength, although in young tectonic domains, such as Tibetan Plateau and the East China Sea Basin, lithospheric structure and tectonics have strong effects on lithospheric strength.