The invention relates to an input current closed-loop amplitude limiting method and system during a grid voltage drop of an air conditioning system. The method comprises the following steps: limiting the amplitude of electromagnetic torque compensation TeComp through an input current effective value and an input current effective value protective threshold value; adjusting the electromagnetic torque given quantity Te_ref through the electromagnetic torque compensation TeComp with limited amplitude to obtain the final electromagnetic torque given quantity for compressor operation; processing the final electromagnetic torque given quantity for compressor operation through a maximum torque/current ratio control module to obtain the direct-axis current given quantity Id_ref and the quadrature-axis current given quantity Iq_ref; performing vector control on a compressor to realize limiting on the input current effective value Iin_rms. According to the method, during the grid voltage drop, the operation efficiency of the compressor is limited through limiting the output electromagnetic torque of the compressor, the effects of reduction of the compressor power and reduction of the input current are realized, the method has a high response speed, the input current is within the overcurrent capacity of an input circuit, the circuit is prevented from being damaged, and normal operation of the system is guaranteed.