A method of upgrading software through a software download in a T-DMB terminal includes the steps of confirming, by the T-DMB terminal, an announcement message containing information for announcing when the software is downloaded by receiving a T-DMB signal and analyzing a plurality of fast information groups (FIGs), determining whether the software is downloaded according to information contained in the announcement message, if it is determined that the software is downloaded, storing ensemble information and download start time information among the information contained in the announcement message; matching a current ensemble with the stored ensemble when time according to the download start time information elapses, and confirming a signaling message for informing that the software is downloaded by analyzing an FIG received through the matched ensemble, and downloading the software.