A method and apparatus for time synchronization and an OFDMA receiver thereof are provided. A preamble timing is obtained by a two-stage correlation in a time domain between a sequence of a received symbol and a reference preamble. The two-stage correlation is further simplified to perform a conjugate multiplication between a one-stage correlation and its correspondingly delayed result. A preamble boundary is adaptively determined by a peak value based on a result of the two-stage correlation. In this way, the time synchronization is achieved with a robust performance in a low SNR, high frequency offset or large delay spread fading channel.