In this paper, a CFO matrix method is presented for carrier frequency offset (CFO) estimation in interleaved uplink orthogonal frequency division multiplexing access (OFDMA) system. The proposed method utilizes the information of eigenvalues and eigenvectors of the defined CFO matrix to estimate the CFOs of all involved users. Compared with the previous works, the main advantages of the proposed approach are that it can obtain the CFOs of all users simultaneously within only one OFDMA block without pilot symbols, provides better performance such as smaller estimation error and superior noise-resistant capability. Simulation results verify the high accuracy and effectiveness of the proposed method.