Potassium nitrate (KNO3) was chosen as the precursor to prepare the K-poisoned catalysts on natural manganese ore using the impregnation method. The results demonstrate that the natural manganese ore catalyst possesses superior alkaline resistance performance with a high NOx conversion for NH3-SCR of NOx at a low temperature. There are two factors responsible for the alkaline resistance performance. Firstly, the NH3 adsorption capacity (more acid sites) of K-poisoned catalysts is stronger than that of fresh catalyst, which is beneficial for the NOx conversion. Secondly, the K-poisoned catalyst has a smaller specific surface area, lower concentrations of Fe3+, Mn4+, and O-alpha, and lower reducibility, which leads to an inhibition effect on the NOx conversion. There exists a competition mechanism between the promotional and inhibition effect on the NOx conversion. The combination of these two effects leads to natural manganese ore exhibiting a superior alkaline resistance performance.