Abstract: Converter station is the associated area of the coupled AC and DC system. There are many equipment in the station and the operation environment is complex. Although the protections of AC filters are relatively complete, the special transient characteristics of electrical quantities under various abnormal disturbances may still cause maloperations of overload and other protections. By analyzing the waveform characteristics of the current on the resistance branch of AC filter under typical overload and inrush current conditions, the maloperation mechanism of AC filter overload protection caused by inrush current is revealed. From the perspective of waveform similarity, combined with Spearman rank correlation coefficient, an auxiliary criterion for AC filter overload protection is proposed. Simulation tests are carried out to verify the effectiveness of the proposed criterion in identifying inrush current disturbances, so as to prevent the maloperation and improve the reliability of protection.