The concerns of distributed generations including photovoltaic(PV) system have been increased around the world since PV system is becoming widespread as a clean and gentle energy source for earth. In the future high density grid-connected PV systems will be interconnected with distribution network. As a result, the stability and long-term reliability of PV systems have become more important issues in this area. Grid-connected PV systems have been installed and monitored at field demonstration test center(FDTC) and also data acquisition system(DAS) has been constructed for measuring and analyzing performance of PV system to observe the overall effect of environmental conditions on their operation characteristics. The performance of PV system has been evaluated and analyzed for component perspective (PV array and power conditioning system) and global perspective (system efficiency, capacity factor, and electrical power energy) by field test and loss factors of PV system.