The invention relates to a 2,3'5,5'-diphenyl tetracarboxylic acid cadmium complex and a preparation method thereof and relates to the field of cadmium complex fluorescent materials. A chemical formula of the 2,3'5,5'-diphenyl tetracarboxylic acid cadmium complex is {[Cd2(bptc)(bih)(H2O)2].H2O}n, wherein bptc is 2,3',5,5'-diphenyl tetra formic acid anion ligand, and bih is 1,6-di(imidazole-1-) hexane. The preparation method of the 2,3'5,5'-diphenyl tetracarboxylic acid cadmium complex comprises the following steps: under hydrothermal condition, dissolving 2,3',5,5'-diphenyl tetra formic acid, an inorganic base, 1,6-di(imidazole-1-) hexane and a cadmium salt in water, adding the obtained mixed solution into a closed reaction still, heating to 120-160 DEG C at a speed of 10 DEG C per hour, performing heat preservation for 3 days, then cooling to room temperature under natural conditions, so that colourless massive crystals are generated, and then washing and drying, so that the target product, namely the 2,3'5,5'-diphenyl tetracarboxylic acid cadmium complex, is obtained finally. The 2,3'5,5'-diphenyl tetracarboxylic acid cadmium complex has stable fluorescence property and high yield, and the preparation method is simple, and has good repeatability.