Potassium fertilizer was applied on flat peach cultivars ‘Jinxia Pantao’ and ‘Yuxia Pantao’ at three weeks (3W),2 weeks(2W) and one week (1W) before fruit maturation,respectively.The appearance quality,internal quality and vegetative growth weight were analyzed.The results showed that:(1)the fruit volume and single fruit weight were significantly increased upon the application of potassium fertilizer at 2 weeks before maturation (2W).The single fruit weight,cheek diameter and suture diameter of ‘Jinxia Pantao’ with potassium fertilizer application at 2 weeks before maturation (2W) were 11.48%,3.51% and 3.03% higher,respectively than that of 1W.The single fruit weight,cheek diameter and suture diameter of ‘Yuxia Pantao’ with treatment of 2W were 56.86%,14.97% and 3.67% higher,respectively than that of 1W.(2)Potassium application had minor effect on fruit color of ‘Yuxia Pantao’,but significantly increased a^* value of ‘Jinxia Pantao’.The a^* values of ‘Jinxia Pantao’ with treatment of 2W and 3 W were significantly higher than that of 1W,which were increased by 55.02% and 44.49%,respectively.(3)Soluble solid content,sucrose and soluble sugar of ‘Jinxia Pantao’ and ‘Yuxia Pantao’ were all in sequence of 2W>3W>1W,but there was no significant difference in soluble sugar content between 2W and 3W.By contrast,potassium application had minor effect on accumulation of total acid and vegetative growth both in ‘Jinxia Pantao’ and ‘Yuxia Pantao’.These results indicate that the optimum period of potassium fertilizer application was at 2 weeks before maturation.