Surface roughness is the key factor to influence the normal restitution coefficient between particle-wall collision. In addition, surface roughness will reduce the formation of liquid bridge under humid conditions which are strongly related to the value of the capillary force. In this study, both experimental and theoretical analysis are presented to explore the effect of surface roughness on the process of particle-wall collision under different humid conditions. The particle-wall collision is photographed by a high-speed camera system. The experimental results showthat the normal restitution coefficient of the particlewith radii of 3 mu m and 6 mu m decrease within the surface roughness of 19.76-236.92 nmroot mean square (rms) and the relative humidity of 35%-85%. In the theoretical analysis, the capillary force is found to decrease when the surface roughness is less than 20 nm rms, and increase as the surface roughness increases. (C) 2020 Elsevier B.V. All rights reserved.