Radio frequency (RF) imperfections, such as DC offset, frequency offset and I/Q imbalance, are important issues in wireless broadband systems. In this paper, preamble-aided estimation and compensation of I/Q imbalance with filter mismatch are proposed to enhance signal quality and link reliability for 2x2 MIMO-OFDM systems. The proposed preamble-aided estimation is able to detect filter, gain and phase mismatches by using the cross-ratio property of preambles. Then the estimated result is programmed to correct this distortion. Through simulations in frequency-selective fading, they hint that this solution can solve I/Q imbalance with 2 dB gain error, 20° phase error and 180° filter mismatch.