The invention belongs to the technical field of composite material preparation, in particular to Fe-modified nano-manganese oxide / MIL-125 (Ti) catalyst and a preparation method thereof, the steps of the preparation method comprising: A, MnSO 4 , NaClO 3 Ultrasonic mixing with NaCl in deionized water; then adding ferric chloride hexahydrate for ultrasonication; then dripping concentrated sulfuric acid into the solution under the condition of stirring in an ice bath, and reacting in the reactor; B, precipitation with absolute ethanol and deionized water Centrifugal washing, drying, grinding and calcining in a muffle furnace to obtain iron-modified nano-MnOx; C, DMSO and C 3 h 8 After mixing O, add 1,3,5-BTC, nano-MnOx ultrasonic, and then drop into C while stirring at room temperature 12 h 28 o 4 Ti; the solution is put into a reaction kettle for reaction; finally, it is centrifuged and washed with isopropanol and water, and freeze-dried to obtain a composite catalyst. The composite catalyst of the invention can effectively reduce the conversion temperature of nitrogen oxides, improve anti-toxicity and prolong the service life of the catalyst.