The invention discloses an SCR (selective catalytic reduction) monolithic honeycombed catalyst for low-temperature flue gas de-nitrification and a preparation method thereof. The catalyst is prepared by using TiO2 and molecular sieve as carriers, MnO2 and Fe2O3 as main active ingredients, and one or more of ZrO2, NiO, WO3, CoO and CeO2 as auxiliary active ingredients through the following steps of: (1), preparing precursors of the carriers, main active gradients and auxiliary active ingredients, and the additives in proportion, and carrying out dry-mixing; (2), kneading to obtain plastic wet feed aggregates; (3), extruding the plastic wet feed aggregates successively through large sieve plates and small sieve plates or mixing in a vacuum pug mill to obtain compact and even degassed mud section; (4), carrying out extruding molding to the degassed mud section, so as to obtain a monolithic honeycombed catalyst blank; (5), drying the blank, carrying out microwave treatment and then baking. By adoption of the preparation method, the preparation process of the catalyst is simplified, the prepared catalyst does not need to be heated additionally, and the high catalysis activity and excellent waterproof property can be obtained only by heating the catalyst by tail end exhaust gas, therefore, the monolithic honeycombed catalyst is higher in engineering practical application value.