Resonance existing in an active power filter LCL system should be restrained by introducing damping.When the current timer comparison control method is used，the strategy for the filter capacitor with virtual damping in parallel is proved appropriate by contrast and analysis.By detection of harmonic voltage on the filter capacitor，this method is equivalent to a virtual harmonic resistor in parallel with the capacitor under the function of proportional component to enhance the damping effect.The method is easily implemented without differentiation.In addition，a mathematical model is developed and the stability domain of the virtual damping control coefficient is obtained according to the July stability criterion.Firstly，to ensure system's stability，the sampling frequency must be six times greater than the resonant frequency.Furthermore，the stable region is enlarged with an increase of sampling frequency，and narrowed with an increase of resonant frequency or total grid- side inductance.Simulations and experiments have proved the validity of the proposed virtual damping strategy and the theoretical analysis.