Yb-Er co_doped Al2O3 film was prepared on SiO2/Si substrate using a medium frequency magnetron sputtering system, and the concentrations of dopant Er and Yb ions were 0.3% and 3.6%, respectively. The up-conversion mechanisms of Er3+ photoluminescence at 529 and 549nm were discussed. The fluorescence intensity ratio of the green up-conversion spectra were measured in the temperature range of 291.8—573.3K, and the temperature characteristics were fitted as R=5.37exp(-738/T). At the temperature of 366K, the sensitivity has the maximum value of 0.0039 K-1. The results show that the Yb∶Er∶Al2O3 film is a suitable material for minitype, high-sensitivity and high-temperature optical sensors.