The signal transmission and measurement method of the passive UHF radio-frequency identification(RFID) system are discussed in this paper. Part of tags communication performance which conforms with the ISO/IEC 18000-6 Type C was obtained by using the software-defined radio test platform. The received power by the platform changes with the communication parameters. Sensitivity of different tags was tested. All experiments were conducted under normal conditions.The measurement results show that the small Tari, half duty cycle (PW) and higher modulation index in baseband signal encoding allow the RFID system to receive larger power, also the RFID system to have larger read range.