Generalized Tellegen’s theorem is independent of physics attribute and has a bearing on the mathematical models. So it has been applied widely in power system. Considering the photovoltaic grid-connected factors, photovoltaic power can be configured as the PQ node in power flow calculation. According to small disturbance theorem, the new modified equation based on the Generalized Tellegen’s theorem is established on current-influx model basis. Then, according to the established the new modified equation, photovoltaic power is connected to the IEEE30 test system of pipeline. Example analysis demonstrates that the new algorithm is superior to traditional algorithm in calculation speed and iteration number, and it also shows that Generalized Tellegen’s theorem has important application values in power system with photovoltaic power.