Due to wide coverage and high transmission power of digital television (DTV) transmitters, DTV based wireless positioning is a promising complementary to global positioning system. For Chinese DTV broadcasting network whose key technology is time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM), this paper proposes a time-frequency joint positioning scheme by utilising TDS-OFDM signal properties in both the time and frequency domains. The proposed scheme needs no modification of current infrastructures, and has no impact on the normal TV program reception. Simulation results show that the positioning accuracy of less than 0.1 m can be achieved when the signal-to-noise ratio is higher than 20 dB over the realistic simulated channels.