Channel estimation is an important topic in wireless communication. In this paper, channel estimation schemes using pilot signals in the context of MIMO-OFDM systems are investigated. For the existing methods, in order to estimate the channel character between every transmitter and receiver antenna in MIMO-OFDM system, the different transmitter antennas usually send pilot signals alternately in different OFDM symbols. This means that only one antenna sends pilot signals every time, and other antennas must be vacant, just like the pilot module in IEEE802.16c. This means inefficient and inflexible, especially in mobile wireless channel. The proposed method can avoid the above defects. The proposed optimal training sequences can be inserted into every transmitter antenna pilot module synchronously without vacancy based on the MMSE. We can get more information about the mobile wireless channel. Through simulation, it is shown that the optimal pilot sequences derived in this paper outperform both the random and orthogonal pilot sequences that appear to be suboptimal. Furthermore, the proposed method can work even when some transmitters or receivers are disabled, but the existing methods can't.