This application discloses example radio frequency identification systems and example methods for constructing a relay network, a reader, and a repeater. One example radio frequency identification system includes a reader, a repeater, and a target tag. The reader can be configured to send a first signal to the repeater. The repeater can be configured to send an excitation signal to the target tag based on the first signal. The target tag can be configured to send a target backscatter signal based on excitation of the excitation signal, where the target backscatter signal carries electronic product code information. The reader can be further configured to receive the target backscatter signal and obtain the electronic product code information in the target backscatter signal.