This letter presents computationally efficient subspace-based estimators to estimate carrier frequency offset (CFO) for interleaved orthogonal frequency division multiple access (OFDMA) uplink systems. Conventional subspace-based estimators rely on eigenvalue decomposition (EVD) of sample correlation matrix to compute signal subspace or noise subspace. For interleaved OFDMA with large subchannel, conventional subspace-based CFO estimators inevitably lead to intensive computational complexity due to calculating sample correlation matrix and its EVD. To circumvent this problem, in conjugation with center-symmetric trimmed correlation matrix and Nystrom method, the required signal subspace or orthogonal projection matrix only needs to calculate two submatrices of center-symmetric trimmed correlation matrix. Therefore, the proposed signal subspace-based and noise subspace-based estimators not only can estimate CFO, but also save computational cost, especially in high SNR and large subchannel scenarios. Computer simulation results are also provided for illustrating the effectiveness of the presented blind CFO estimators under single OFDMA data block.