In order to fully consider the impact of photovoltaic power generation systems and perform real-time monitoring,a robust state estimation approach for grid-connected photovoltaic power generation systems is proposed.The photovoltaic system model is built, and the corresponding measurement model is developed. Robust state estimation is capable of monitoring the operating state of a distribution network,and reliably estimate the state variables of the system. In this paper, Least Absolute Value (LAV) estimation algorithm is used for robust state estimation, which not only has the ability to reject bad data, but also has high computational efficiency.The simulation results show that the method can effectively estimate the operating state of the photovoltaic system with good convergence properties, and is of the robustness enabling the detection and identification of bad data in the photovoltaic system.