Reducing the performance degradation of air source heat pumps (ASHPs) due to frosting during the heating season is critical. Previous studies have reported that a higher Characteristic Index for Configuration and Operation (CICO) improves the frosting suppression performance of ASHPs. However, selecting appropriate CICO for different regions is a challenge due to their varying frosting suppression needs. This study proposes two frost suppression grades (FSG 1 and FSG 2) to define acceptable levels of frosting loss, and develops a novel CICO design method based on the CICO-based equivalent temperature drop approach. Taking 161 high-humidity cities in China as examples, the study assesses the impact of different CICO on frosting losses, and determines the recommended CICO value for each region. Results indicate that increasing the CICO from 6 to 10 reduces frosting losses by an average of 37.5% in high-humidity regions, and raises the proportion of cities meeting frost suppression grades from 17% to 80%. To meet FSG 2, CICO values of 8 to 17 are generally sufficient, while achieving FSG 1 requires CICO values above 10 in 90% of cities and above 30 in 17 cities. These findings offer practical guidelines for the efficient application of ASHPs in high-humidity regions.