The present invention provides a time-frequency code spreading method in an OFDMA system. The method includes: converting a transmission message into one or more modulating signal vectors, and each bit of the transmission message is spread onto all vector elements of a modulating signal vector; mapping one or more modulating signal vectors to a set of time-frequency grids, wherein in an OFDMA time-frequency plane, two time-frequency grids to which any two vector elements in each modulating signal vector are mapped do not have the same frequency location or time location. In addition, the present invention also provides a time-frequency code spreading apparatus in an OFDMA system.