Three-phase grid-connected inverters are usually digitally controlled, and due to the negative damping effect brought about by the digital control delay, grid-connected inverters are prone to interact with the grid impedance (capacitive reactance) to produce high-frequency harmonic resonance when they are connected to the grid, which seriously affects the safe and stable operation of the power system. For the negative damping problem brought about by the controller delay, the low-frequency coupling effect of the inverter is ignored, and a high-frequency impedance model is established to reveal the high-frequency resonance mechanism, and the results show that the negative damping brought about by the delay exists a high-frequency resonance risk in the resonance peak interacting with the grid impedance. To improve the high-frequency resonance stability, based on the idea of passive design of the control loop, an approximate high-frequency passive composite impedance shaping is carried out for the grid-connected current loop control, and the parameter design process is given. An approximate high-frequency negative damping offset is achieved by modifying the control loop to enhance the stable operation capability of the system. Finally, the effectiveness of the proposed method is verified with Matlab/Simulink.