Cemented Paste Backfill (CPB) technology has been effective in using the tailings to refill the underground cavities. The wet or dry rock surface can significantly affect the stability of the CPB-Rock interface, and the shear loadbearing capacity of CPB-Rock interface always reflects the overall stability of the filled underground cavities. Therefore, clear understanding on the shear behavior of the CPB-Rock interface with wet or dry rock surface is very important. To investigate the shear behavior of CPB-Rock interface with different rock surfaces (wet and dry), an apparatus for shear tests at CPB-Rock interface was constructed by modifying the servo-controlled GCTS (Geotechnical Consulting & Testing System) loading frame. Over 72 CPB-Rock samples with dry and wet rock surfaces were tested under four confining pressures (0, 50,100 and 150 kPa) and different curing time (1, 3, 7 days). The findings show that, under the same confining pressure and curing time, the shear strength of the CPB-Rock interface with the dry rock surface is much larger than that of the wet one. Furthermore, with the increase of the curing time under a same confining pressure, the increase of shear strength on the dry rock surface is also larger than that of the wet one due to the presence of water film on the wet rock surface. The shear strength is enhanced with the increase of confining pressure. Further, the testing results were analyzed within the framework of the Mohr-Coulomb criterion, which comply with the corresponding theoretical curve. It is concluded that the dry rock surface is essential to the stability of the filled underground cavities. In case of wet environment for the underground cavities, it is important to find ways to dry the rock surface before carrying out back filling using CPB method. (C) 2020 Elsevier B.V. All rights reserved.