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We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy, combining high pressure and high temperature (HPHT) reactive sintering with appropriate ratio of coarse Ti to nanosized TiO2. Ubiquitous lattice defects engineering has also been achieved in our samples by HPHT. The thermoelectric performance was significantly enhanced, and rather low thermal conductivity (1.60 W m−1 K−1) for titanium oxide was reported here for TiO1.76. Correspondingly, a high dimensionless figure of merit (zT) up to 0.33 at 700 °C was realized in it. As far as we know, this value is an enhancement of 43% of the ever best result about nonstoichiometric TiO2 and the result is also exciting for oxide thermoelectric materials. The moderate power factor, the significantly reduced thermal conductivity and the remarkable synergy between electrical properties and thermal conductivity are responsible for the excellent thermoelectric performance. We develop a facile strategy for preparing multi-scale hierarchical TiO2-x and its superior ability to optimize thermoelectric performance has been demonstrated here.