Particle image velocimetry (PIV) is used to study the horizontal channel flow over smooth and rough walls, and single-phase flow and particle-laden flow with two different particle diameters are analyzed. The phenomenon of the wall similarity hypothesis is verified in single-phase flow but affected by particles in particle-laden flows. The pyramidal rough elements cause a velocity defect and shorten the length scale of the vortex. The streamwise and wall-normal Reynolds stresses are enhanced by wall roughness. Two kinds of particles with different Stokes numbers are used in the experiment. The collision and dragging effect of particles in the inner region offset the influence of wall roughness on the mean velocity profile. The introduction of particles tends to increase the streamwise Reynolds stress, but makes the peak of the Reynolds stress move to a higher wall-normal position, which is contrary to the effect of wall roughness. Quadrant analysis indicates that the wall roughness and particles show a converse effect on quadrant events, but neither change the majority of second and forth quadrant events. The analysis of the spatial structure of turbulence shows that the small scale spatial structure is less affected by wall roughness compared with the large scale spatial structure. According to the statistics of the particle distribution, it was found that particles with a larger Stokes number show a more distinct prioritized deposition in the inner region, and the deposition of particles is reduced due to the existence of rough elements. (C) 2019 Elsevier B.V. All rights reserved.