Generally, precipitation with pH less than 5.6 is considered acid rain, which will have adverse effects on water, soil, animals, and plants, etc, therefore, rapid detection of acid rain is of great significance. In this work, the rare earth europium is combined with 4,4,4-trifluoro-1-phenyl-1,3-butanedione to obtain the Eu 3+ complex, Eu(BTA) 3 (H 2 O) 2 . As an auxiliary ligand and matrix, ethyl cellulose avoided the fluorescence quenching caused by uneven dispersion of the complex in the matrix and while sensitizing the fluorescence of Eu 3+ . The rare earth complex light-conversion film is successfully prepared. The results showed that the film has good responsiveness to pH value. In the process of neutral to acidic aqueous solution, the fluorescence is gradually quenched and exhibits a good linear relationship, when the aqueous solution changed from acid to neutral, the fluorescence will be restored, and the fluorescence intensity can still maintain above 90% after 5 repetitions. In addition, the light-conversion film has excellent light conversion ability and high color purity. It can transform harmful ultraviolet light into red light which is conducive to photosynthesis, as well as prevent damage of acid rain to plants and has a certain positive effect on agricultural production.