LCL filters are increasingly used in grid-connected photovoltaic inverters as the preferred option. Its inherent resonance character makes the damping strategy a hot topic for research. LCL filter， inverter and the grid are modeled and studied as a whole. The commonly used virtual resistor method of passive and active damping， the impacts of inverters behavior and the grid stiffness on the damping effect are studied in detail. The results show that the non-ideal characteristics of the grid， the proportional gain and the control delay affect the damping properties the most. A hybrid damping method combining active and passive damping is proposed. The method can reduce the impact of control delay and is adaptable for grid change. Experimental results show its effectiveness.