The five series for the Yb³⁺/Er³⁺ co-doped Al₂O₃ films with constant Er³⁺ concentration have been prepared on the SiO₂/Si water by medium frequency magnetron sputtering. The photoluminescence (PL) of the thin films between 1.430 μm and 1.630 μn were investigated under room temperature.Experimental results showed that Ytterbium co-doping efficiently increased the PL peak intensity,and the PL intensity of optimal concentration for 1.OOmol % Er³⁺ and Yb³⁺ ∶Er³⁺ ratio of 10 ∶1 enhance by a factor of about 40,compared with that of 1.OOmol% Er³⁺ doped film;there existed the optimal Yb³⁺/Er³⁺ ratio with constant Er³⁺ concentration,this mainly was an interacting result of energy transfer and back energy transfer between Yb³⁺ and Er³⁺,whereas the optimal Yb³⁺ /Er³⁺ ratio decreased with increasing the Er³⁺ concentration;the change trend of PL peak intensity for only Er³⁺ oped film was similar with Gauss figure whereas that for Yb³⁺/Er³⁺ co-doped film was similar with anti-Gauss figure as a function of Er³⁺ concentration.