For the grid-connected photovoltaic（PV） power plant and other alternative energy power plants， the electricity must be produced totally from the designated primary energy form due to its special high tariff priority. Such plants must be monitored by the existing energy data acquisition and supervisory system of grid company regardless of capacity or voltage level. Since complicated power， energy exchanges and complicated settlement relationship may exist between the grid-connected PV power plant and power grid， apart from the general requirements for monitoring power， energy exchange， and power quality， a special task is to monitor the PV generation characteristics and possible maximum power generated from PV power plants to prevent the energy measurement errors and inappropriate power generation. A comprehensive， accurate， economic and practical power generation model is necessary. A PV battery theoretic model with the steady parameters provided by the general component supplier is selected. Then， a plant level power generation model is built based on the topology of the main equipment elements. Finally， the identification method of calibrated parameters based on the historical data is also provided. The model has been verified by a real operated PV power plant， and a satisfactory performance is demonstrated.