The invention discloses a method for a long-term evolutionary system to map a resource unit to a resource block; the method comprises the following steps: all available sub-carriers are divided into N RB DL resource blocks with the same size and every resource block comprises N symb DL continuous orthogonal frequency division multiplexing symbols; N sc RB continuous sub-carriers in every orthogonal frequency division multiplexing symbol are included in the resource block, thus every orthogonal frequency division multiplexing symbol comprises N symb DL*N sc RB resource units; the available sub-carriers are respectively set with a logical number k and the resource blocks are respectively set with a logical number nPRB and the orthogonal frequency division multiplexing symbols are respectively set with a logical number l; the combination of the logical numbers of the sub-carrier and the orthogonal frequency division multiplexing symbol is used for representing the resource unitwith the range of k from 0 to N RB DL*N sc RB-1 and the range of l from 0 to N symb DL-1; the logical number k of the available sub-carriers and the logical number nPRB of the resource blocks are utilized to map the resource units to the resource blocks.