The microstructure, superconductivity, and the superconducting current-carrying properties of YbxY1-xBa2Cu3O7-y are investigated systematically. We find that, when the content of Yb increases, Tc changes slightly, but the critical current density decreases with the grain size obviously. The results suggest that just decreasing the grain size can not increase the critical current density of such granuler superconductors in which the couplings among grains are weak.