The surface conductivity of polished polycrystalline diamond films after atomic hydrogen bombardment for different time was compared and the carrier transport characteristic beneath the H-terminated diamond film surface was investigated correspondingly. It is found that, as the bombardment time increases, the surface roughness of diamond films first decreases due to disappearance of scratches, and then increases because of appearance of protrusions produced by plasma preferentially etching. Meanwhile the total C H bonding concentration on the diamond surface increases gradually until it is saturated when the bombardment time is up to 30 min. The almost invariable carrier density is obtained for all samples treated for different time, which indicates the monohydride (CH) mode responsible for surface conductivity forms when hydrogen treatment starts. While for the carrier mobility, it shows the inverse trend with change of the surface roughness. A model based on the surface roughness scattering was proposed to explain the relationship between the surface conductivity and roughness. Combining with the carrier mobility and density, the lowest square resistance of 13.85 K Omega is obtained for polycrystalline diamond film when it is treated for 30 mm. It is speculated that the surface conductivity can be further enhanced by reducing the surface roughness. (C) 2013 Elsevier B.V. All rights reserved.