Channel estimation is a key issue in Time Domain Synchronous-Orthogonal Frequency Division Multiplexing (TDS-OFDM) system, which is usually based on pseudorandom noise (PN) sequences time domain correlation. However, in space time block coding (STBC)-based TDS-OFDM MIMO system, PN sequences received in each receiver antenna are the overlaps of multiple transmitters' linear convolution of PN sequences with corresponding channel responses. Thus, channel state information (CSI) can not be estimated accurately only by means of PN sequences time domain correlation. In this paper we propose a joint time-frequency domain channel estimation scheme for STBC-based TDS-OFDM MIMO system with 2 transmitter antennas and 2 receiver antennas. To aid the channel estimation, every two signal frames in a super frame are grouped into a signal frame group at the transmitter side. For the first frame of each signal frame group, 315 Transmission Parameters Signaling (TPS) symbols are inserted equally with 12 OFDM sub-carries intervals in both transmitter branches. While for the second frame, TPS symbols are inserted equally only in the first transmitter branch, and in the second transmitter branch zero symbols are inserted in the corresponding positions. By exploiting such an elaborate TPS inserting rule and PN sequence time domain correlation, our proposed scheme can estimate CSI easily in both time domain and frequency domain. Simulation results show that our scheme can estimate the CSI accurately: the mean absolute error between the estimated values and the original values is less than 0.01 under slow-fading channel when the signal-to-noise ratio (SNR) is 8 dB.