Field experiment with four levels of nitrogen ieN0(no nitrogen),N1(150 kg/hm2),N2(300 kg/hm2)and N3(450 kg/hm2)were set to explore the relationship between nitrate content in leaf petiole and yield,total N content in leaf,total N content in plant and aboveground biomass.Nitrate of new features leaf petiole was measured using reflectometry method and aboveground biomass and economic yield were also measured.The result showed that the optimized nitrogen application(N2)economic output was 95 259 kg/hm2,which was 50 812 kg/hm2 and 14 988 Yuan/hm2 higher than nonfertilized treatment(N0)in yield and income.Petiole nitrate concentration in all the treatments had the same trends along with the growing process,and the petiole nitrate content among treatments was N0＜N1＜N2,which showed it increased with the increasing amount of nitrogen fertilizer in a certain range.After proof testing,the prefull fruit period of tomato was the reasonable period for nutrient diagnosis,and the diagnostic threshold was 4 182 mg/L.Meanwhile a topdressing model based on petiole nitrate content was established.