Carrier frequency offset (CFO) largely degrade the performance of orthogonal frequency-division multiplexing (OFDM) systems because they may violate the orthogonality of sub-carriers and introduce the inter-carrier interferences. In this paper, by using some special pilots which take value from a constrained set and are interspersed in frequency-domain subjected to a specified distribution, CFO of a MIMO-OFDM system is estimated. The studies in theory and experiment show that the new CFO estimator provides a satisfactory performance in estimating CFO and is better appropriate for tracking CFO than the existing approaches.