The pseudo-layered GeTe-rich Sb2Te3(GeTe)n (GST), with an unique kind of Te-Te gaps in the unit cell, is found to have promising thermoelectric performance. In this talk, we will report an ultrahigh figure of merit ZT value ~2.4 at 773 K and average ZT ~1.5 between 323K to 773K for the p-type pseudo-layered Sb2Te3(GeTe)17 sample along the parallel direction by synergistically optimizing its electrical and thermal properties via vacancy engineering. The microstructural origin of thermoelectric property enhancement was studied by aberration-corrected transmission electron microscopy. The results by in situ characterizations revealed that upon annealing Ge vacancy gaps in quenched samples tend to migrate and recombine into long-range gaps. The recombination of Ge gaps would lead to an overall reduction of carrier concentration which took an optimizing to the power factor, reaching a high value plateau of ~45 μW cm-1 K-2 from 623 K to 773 K. Moreover, the abrupt decrease of carrier concentration resulted in a sharp reduction of the electrical thermal conductivity κe and the formed long range Van der Waals gaps contribute to the reduction of lattice thermal conductivity κl, approaching a low total thermal conductivity ~1.4 W m-1 K-1. The stable high performance offered by Ge vacancies engineering provided a promising approach in the future research in GST materials.