Provided is an apparatus and method for detecting a time-frequency code in an MB-OFDM UWB system. The apparatus includes a controller for providing a band selection signal to the RF receiver and outputting a preamble selection signal at regular symbol periods to calculate a cross correlation value for a predetermined time period more than a beacon frame interval when a time-frequency code search start signal is received; and a cross correlator for storing information on preamble patterns, selecting a preamble stored depending on the preamble selection signal, and calculating a cross correlation value for a digital signal transferred through the RF receiver, wherein the controller determines a time-frequency code using a preamble where a peak occurs as a time-frequency code that is currently in use when a peak signal is inputted based on the calculated cross correlation value, and transmits the determined time-frequency code to the MAC receiver.