Yb3+ singly doped and Yb3+/Al3+co-doped high silica glass samples are prepared, and their luminescent properties are investigated. Al3+ is considered as a beneficial activator for Yb3+-doped glass. However, the experimental result shows that the addition of Al3+ results in the transformation from Yb3+ to Yb2+ and the improvement in the photon luminescence of Yb2+. These characteristics indicate the role of Al3+ in Yb3+-doped glass.