In MIMO OFDM communication systems, perfect channel estimation is required for the coherent demodulation. In conventional space time processing algorithms, signal detection is always performed after the channel estimation process is finished. When channel estimation error exists, the performance of signal detection degrades greatly. In this paper, we propose an iterative signal detection algorithm which can jointly performs the channel estimation. Compared with conventional channel estimation and signal detection approaches, this algorithm can improve the channel estimate accuracy and therefore enhance the signal detection performance. In our work, the algorithm is employed in both space time coded and V-BLAST structured MIMO-OFDM systems. Simulation results and analyses show that this kind of joint estimation and detection strategy is more bandwidth efficient and can significantly improve the system performance under fast fading multi-path channels.