Power fluctuation caused by irradiance changes may cause the flicker at the grid-connected point. The relationship between the flicker and grid impedance, the power change amount is analysed. And the flicker is tested on a 500kW photovoltaic (PV) inverter at different load and switch operation. Based on the vitual gird model and the flickermeter model developed on Matlab/Simulink platform, the flicker test results of switching operation and continues operation are analysed.