Er3+:Yb3+ co-doped oxy-fluoride glasses with composition of (50-x) GeO2.PbF2.WO3.(6 + x) CdF2.1.4Yb2O3.0.6Er2O3 (x = 10,20,30) were prepared. Their up-conversion fluorescence characteristics were investigated under excitation of 930 nm diode laser. Three strong fluorescence bands of Er3+ whose central wavelength lie in 543, 550 and 655 nm have been observed. The maximum phonon energy is obtained by measuring anti-stokes Raman shifts of the samples, and the up-conversion mechanism is briefly discussed. The influences of host materials composition on up-conversion efficiency are also discussed adopting the average electronegative difference and the cationic field strength of the host. It is found that relative small average electronegative difference and large cationic field strength of host benefit to energy up-conversion.