Relative to its size, tropical Asia is likely to be the richest region in terms of biodiversity. However, the factors of species diversity formation and maintenance in Southeast (SE) Asia and neighboring regions remain poorly understood. Here we infer the evolutionary relationships within psilodercid spiders by incorporating fossil information into a robust, unprecedentedly complete species-level phylogeny of 202 extant species to explore potential abiotic drivers and ecological features underlying their stable diversification history. The combination of extant and extinct historical biogeographic data indicates that in situ speciation is the predominant form of diversification in tropical Asia but diverse Cretaceous psilodercids in Myanmar ambers were replaced by other biogeographical lineages during the northward movements of the Burma Terrane. Furthermore, our diversification analyses show no diversification rate changes through time and across geographic space in this family, but the genus Althepus displays an accelerated rate of species diversification driven by the remarkable expansion of leg length. Trait evolution analysis shows that ecological trait divergence contributes to the diversification and accumulation of tropical spiders by facilitating species coexistence. These findings provide empirical evidence that the ecological trait divergence over evolutionary time scales is key to forming species diversity hotspots in SE Asia. Thus, this study integrating molecular evidence and paleontological interpretation provides a new framework for understanding the evolution of tropical species diversity.