The invention discloses a binder, which comprises the following component contents in percentage by weight: 20-85 percent of bentonite and 15-80 percent of cement. The application of the binder in a catalyst for removing nitric oxide in smoke gas comprises the following steps of: fully mixing the binder with catalyst powder for removing the nitric oxide in the smoke gas according to the mass ratio of 0.18:1-0.25:1; adding water content, and mixing into slurry; and uniformly coating on slide glass, and drying at 150-300 DEG C. The binder is low in cost and is safe without toxicity, and the application method of the binder in the catalyst for removing the nitric oxide in the smoke gas is simple, and the prepared flakes have better denitration performance, with certain intensity and water resistance ensured at the same time.