In order to obtain a better performance of joint estimation frequency offsets (CFOs) and timing errors (TEs) for the uplink transmission of Orthogonal Frequency Division Multiple Access (OFDMA) companied with a generalized carrier assignment scheme, the use of Constant Amplitude Zero Auto Correlation(CAZAC) sequence and increasing the number of training blocks improve the existing algorithm of joint estimation.Although the efficiency of transmission is reduced, the performance of estimation has improved and this sacrifice is worth it. Simulation results show that the performance of improved algorithm of estimation is better than the original algorithm and its application range is more extensive.