Nitrogen (N) and potassium (K) are essential macronutrients for plants growth; however, the mechanism by which K mediates negative effects on ammonium-sensitive plants is still poorly understood. We hypothesized that K supplies may enhance antagonistic ammonium stress while improving nitrate nutrition function, which wheat seedlings were grown in sand culture in the presence of two N forms (ammonium; nitrate) supplied at two rates (2, 10 mmol L-1) and three K levels (0.5, 5, 15 mmol L-1). We found that a high N rate increased plant biomass under nitrate nutrition, while it had a negative effect under ammonium nutrition. Compared with nitrate, biomass was depressed by 54% or 85% for low or high N rate under ammonium. This resulted in a reduction in gas exchange parameters and a subsequent decrease in growth variables and nutrient uptake, whereas these parameters increased significantly with increasing K levels. Moreover, in principal components analysis, these variations were highly clustered under nitrate nutrition and highly separated under ammonium nutrition. Our study shows a clear positive interaction between K and N, suggesting that high K supply relieves ammonium stress while improving growth vigor under nitrate nutrition by enhancing nutrient uptake and assimilate production in wheat plants.