Abstract: The effects of N, P, and K. with respect to their rate and ratios, on the yield and quality of sweet corn were studied by quadratic regressive orthogonal combinatorial design. The results showed that the yield of commercial fresh ear could be significantly increased by applying N, P and K fertilizers in the order of N>K>P. Under the experimental condition, maximum yield (9. 6 t/ha)was obtained by a combination of 273. 0 kg N/ha, 94. 5 kg P2O3/ ha and 270. 0 kg K2O/ha, and the water-soluble sugar content of frest seeds was markedly increased with increasing K. The minimum content of water-soluble sugar was found in fresh seeds as the combination of 100. 5 kg N/ha arid 75. 0 kg P2O5/ha. Below this level, the sugar content was decreased with the increase of N and P; over this level, the sugar content was increased with the increase of N and P. With regard to considering the yield of fresh ears and the sugar content of fresh seeds, a suitable ratio of N, P and K was recommended as 273. Okg N/ha. 94. 5kg P2O3/ha and 270. Okg K,O/ha, as N, P2O3, K2O= 1 : 0. 35 : 1.