Broadband PLC (power line communication) has become one of the most important communication technologies for Smart Gird applications, especially for AMI (Advanced Metering Infrastructure) and HAN (Home Area Network). Currently, most broadband PLC products are based on OFDM, DMT or Spread-Spectrum technologies. Their performances differ from each other on certain circumstances. This paper proposes a performance testing model to test PLC devices' Transmitting Capacity and Noise Tolerance. Four PLC devices using different modulation technologies respectively are tested. In addition, the performances of different technologies are analyzed and some discussions are made. To reduce the affection of noise brought in by electric appliances, an “isolating socket” is introduced, which can filter the noises on the appliance side.