By the method of comparative analysis of fluorescence spectra, fluorescence enhancement of europium(III) was studied in aqueous solution with trimellitic acid (benzene-1, 2, 4-tricarboxylic acid (TLA)) as ligands. The results showed that the ligand sensitized improved the fluorescence intensity three orders of magnitude in aqueous solution at pH 6.3, and with surfactant TritonX-100 in aqueous solution at pH 6.7, rare earth La3+ increased the fluorescence intensity furtherly about two orders of magnitude. Both intermolecular and intra molecular energy transfer modes were applied to explain the cofluorescence mechanism of the system under the different test conditions. In the optimum determining conditions, when Eu3+ concentration was in the range of 6.7×10-8～5.0×10-6 mol/L, it had a linear relation with the fluorescence intensity of Eu3+-La3+-TLA-TritonX-100 system, and the limit of Eu3+ in the system was detected to be 8.0×10-9 mol/L.