The invention discloses a preparation method for a lignite semi-coke-based denitration agent used for low-temperature catalytic oxidation. The method prepares lignite semi-coke through high-temperature carbonization; then the lignite semi-coke is used as a carrier, and an alkaline substance and metal oxide are loaded as active components for modification; and ultrasonic equal impregnation is carried out to prepare the modified lignite semi-coke-based catalyst. The catalyst allows the conversion rate of NO to NO2 under catalytic oxidation to reach 87% at a reaction temperature of 100 DEG G; the catalyst has low catalytic activity and can be used for removing NO from a low-temperature emission source of aerobic waste gas; the method has the advantages of simple process, convenient operation, low operation cost, no need for high temperature and no use of an oxidant; and the catalyst prepared by the using the method has a high NO removal rate.