The impact of humidity on the characteristics of the ground total electric field in HVDC transmission lines is of great significance for line design and environmental protection assessment. In this study, transverse measurements of the ground total electric field distribution under varying humidity conditions were conducted using an indoor reduced-scale test line. The results reveal that humidity exerts a distinct polarity-dependent effect on the ground total electric field distribution. Specifically, humidity significantly influences the ground total electric field distribution during negative corona discharge, whereas its impact during positive corona discharge is minimal. Notably, as humidity increases, a substantial reduction in the ground total electric field is observed.