The invention relates to a preparation method of an SCR flue gas denitration catalyst and a product thereof. The method comprises the following steps: taking slag with potassium manganate extracted as a main raw material, washing the slag with 2mol/L salpeter solution, and filtering, drying and crushing the slag; fully mixing filter residue powder, porous agent powder and electrolytic manganese anode mud, adding in distilled water rubbed strip to prepare particles; and sequentially drying, calcining to carry out activation, and finally preparing the SCR flue gas denitration catalyst. The invention not only saves the raw material cost, but also eliminates the pollution of the waste containing high-valent manganese to the environment, and has the advantage of simple preparation process. Verification proves that the catalyst can play a catalysis role when the flue gas temperature is about 200DEG C, and the service life of the activity catalyzed by the catalyst is also prolonged. Therefore, the invention is a preparation method and a product which have low cost, are beneficial to the environment and can turn the waste into valuable.