The present invention discloses a data transmission method, where a data processing apparatus is connected to multiple remote base stations and one central site device, where the data processing apparatus is connected to each remote base station through one optical fiber or one pair of optical fibers, and the data processing apparatus is connected to the central site device through one optical fiber or one pair of optical fibers, and the method includes: receiving, by the data processing apparatus, at least two data flows transmitted from at least two remote base stations among the multiple remote base stations, aggregating the at least two data flows into one flow of output data, and transmitting the output data to the central site device; or receiving, by the data processing apparatus, one flow of synthetic input data transmitted from the central site device, restoring the synthetic input data to at least two data flows before synthesis, and transmitting the restored at least two data flows to corresponding remote base stations. The solutions provided in embodiments of the present invention reduce the required amount of optical fibers.