PbTe-based compositions are considered as excellent thermoelectric materials for the mid-temperature. However, the toxicity of lead limits its wide application. SnTe compounds, an analogue of PbTe, has attracted much attention. However, its ultrahigh carrier concentration and the large lattice thermal conductivity leads to a low ZT value of SnTe. In this work,thethermoelectric performance of SnTe is synergistically enhanced by introduction of Sn and SnO₂ from the disproportionation of SnO in the process of the hot press sintering. On the one hand, Sn can compensate the Sn vacancies and decrease the carrier concentration of SnTe, leading to a simultaneous enhancement on resistivity and the Seebeck coefficient. For instance, compared with the pristine SnTe, resistivity and the Seebeck coefficient increases from 6.5μΩ•m to 10.5μΩ•m and from 105μV•K^-1 to 146μV•K^-1,respectively, for the sample of SnTe-6mol% SnO at 873K. On the other hand, in-situ generated SnO₂ nanoparticles are dispersedly distributed on the grain boundaries, leading to the multiscale phonon scattering and the reduced lattice thermal conductivity. The minimum lattice thermal conductivity value is 0.6 W•m^-1•K^-1 for the sample SnTe-6mol% SnO at 873K, which is ~33% reduction compared with that of the pristine SnTe. As a result, the maximum ZT value of 0.96 (~100% enhancement, compared with that of the pristine SnTe) at 873K is achieved for the sample SnTe-6mol% SnO.