The effect functions of NPK application on economical yield,fertilization profit of water spinach(Ipomoca aquatica Forsk) were studied by the field experiments with 3414 best regression design.The results showed that the best NPK application of water spinach with maximum economical yield of 31392.4 kg/hm~2 was N 223.6,P_2O_5 50.0 and K_2O 97.5 kg/hm~2,the best NPK application with the best fertilization profit of 36211.8 yuan/hm~2 and higher economical yield of 31360.1 kg/hm~2 was N 215.7,P_2O_5 46.4 and K_2O 90.0 kg/hm~2.Under equal fertilizer,there was significant positive correlation between different N levels and nitrate content;There was significant negative correlation between different P,K levels and nitrate content.