本文研究了氮、磷、钾的用肥量对西瓜光合代谢、根系活力、糖代谢酶活性、瓜果中游离氮基酸含量及结瓜数与瓜果膨大速率的影响。结果表明,三要素中以氮肥对西瓜光合强度的影响最为敏感,而磷钾肥的影响相对平稳些.氮肥对叶片中磷酸蔗糖合成酶和蔗糖合成酶的影响不明显,但氮肥用量过多会提高酸性蔗糖转化酶的活性;增施磷肥能提高酸性蔗糖合成酶和蔗糖合成酶的活性,对酸性蔗糖转化酶的影响不明显:增施钾肥会提高蔗糖合成酶的活性和降低酸性蔗糖转化酶活性。西瓜中各种游离氨基酸含量对西瓜风味品质有显著的相关性。增施氮肥会提高苦味氨基酸含量,降低甜味和鲜味氨基酸含量:磷肥对各种氨基酸的影响趋势类似氮肥,但相对更平缓;增加钾肥用量能降低苦味氨基酸含量,而提高鲜味氨基酸含量.西瓜结果数对钾肥最敏感,而西瓜膨大速率受氮肥影响最大. In this paper, the effects of N, P and K fertilizers on photosynthetic metabolism, root activity, carbohydrate metabolic enzyme activities, free amino acids in fruits and vegetables, number of melon seeds and fruit enlargement rate were studied. The results showed that the three factors were most sensitive to the photosynthetic intensity of watermelon, while the effects of phosphorus and potassium fertilizer were relatively stable.The effect of nitrogen fertilizer on sucrose synthase and sucrose synthase in leaves was not obvious, but too much nitrogen fertilizer would increase The activity of sucrose invertase was increased. The application of phosphate fertilizer could increase the activities of acid sucrose synthase and sucrose synthase, but had no obvious effect on acid sucrose invertase. Increasing of potassium fertilizer could increase the activity of sucrose synthase and decrease the activity of sucrose invertase . The content of various free amino acids in watermelon had a significant correlation with the flavor and quality of watermelon. Adding nitrogen fertilizer will increase bitter amino acid content and reduce sweet and umami amino acid content. The effect of phosphate fertilizer on various amino acids is similar to that of nitrogen fertilizer, but it is relatively more gentle. Increasing the amount of potassium fertilizer can reduce bitter amino acid content and increase flavor amino acid content. The results of watermelon were the most sensitive to potash fertilizer, while the watermelon expansion rate was the most affected by nitrogen fertilizer.