Abstract: Tomato ‘Kuiguanhongfeng’ was used as the experimental material, perlite/vermiculite（V/V 2∶1） was used as the matrix, and ammonium nitrogen(0 mmol·L^-1)+nitrate nitrogen(15 mmol·L^-1)（A0 N15,control）,5 mmol·L^-1+10 mmol·L^-1（A5 N10）,7.5 mmol·L^-1+7.5 mmol·L^-1（A7.5 N7.5）,10 mmol·L^-1+5 mmol·L^-1（A10 N5）,15 mmol·L^-1+0 mmol·L^-1（A15 N0）,were designed.The aim of the study to explore the effect of different ratios from ammonium nitrogen and nitrate nitrogen on growth and ammonium assimilation of tomato under the same nitrogen level, in order to provide a reference for realizing the high efficiency ammonium assimilation.The results showed that compared with the control, the total dry weight were increased by 27% and 20% in A5 N10 and A7.5 N7.5 treatment, was no significant difference in A10 N5 treatment, but was decreased by 22% in A15 N0 treatment.It was found that the content of total free amino acids in roots and leaves were increased by more than 40% with the increase of ammonium nitrogen ratio.The activities of glutamine synthetase（GS）,glutamate synthetase（GOGAT） and glutamate dehydrogenase（GDH） involved in nitrogen metabolism in roots were significantly higher than those in control.At the same time, the contents of glutamine（Gln） and glutamic acid（Glu） were increased with the increase of ammonium nitrogen ratio, but the contents of Glu were decreased significantly with the treatment of A10 N5 and A15 N0,and the contents of soluble sugar, starch and chlorophyll were decreased.It was concluded that when the concentration of ammonium nitrogen in nutrient solution reached 10 mmol·L^-1 or above, the plant growth was inhibited, which may be due to the insufficient carbon assimilation caused by the decreased of chlorophyll content in leaves, which due to the inhibition of nitrogen assimilation caused by the decrease of Glu content, which inhibited the plant growth and reduced the biomass.