The strong blue 476 nm cooperative upconversion luminescence of ytterbium Yb3+-Yb3+ clusters in Yb3+-doped oxyfluoride glass was studied. The strength of this luminescence was found to be about 100 times greater than that of Yb(3): zirconium, barium, lanthanum, aluminum, and sodium fluoride glass. Such a large enhancement of cooperative upconversion blue luminescence efficiency results from better coupled Yb3+-Yb3+ clusters, less cross relaxation, increased concentration of Yb3+ activators, nonsaturation effect, and better upconversion luminescence efficiency. Interestingly, the quadruple-quadruple interaction or exchange interaction seems to exert a stronger action than the dipole-dipole interaction. Meanwhile there apparently exists a large energy transfer from a single Yb3+ ion or a coupled Yb3+-Yb3+ cluster to a Ho3+ ion, leading to a dramatic decline in the intensity of the upconversion luminescence of Yb3+-Yb3+ clusters in an Yb3+-Ho3+ codoped oxyfluoride glass.