A transmit diversity method applied to a transmitting system includes the steps of: receiving a serial stream, and transforming the serial stream into a plurality of parallel streams, wherein each parallel stream is carried by a corresponding sub-carrier; and in light of each sub-carrier, selecting a single transmission path from at least two transmission paths of the transmitting system so as to transmit the parallel stream carried by the sub-carrier. The transmit diversity method further includes the step of: dividing the plurality of parallel streams carried by the sub-carries into M groups, wherein the parallel streams belonging to the same group are transmitted via selecting the same transmission path.