A series of pot experiments were conducted to understand the effects of fertilizer amount on the growth，SPAD，the peroxidase activity，root activity and ultrastructure of leaves of tomato The results indicated plant height at flowering and fruit enlargement period were decreased by 7.66% and 9.84%，stem diameter decreased by 4.58% and 17.05% for the treantment of application of N 0.8 g/kg soil，K2O 0.88 g/kg soil compared with the application of N 0.2 g/kg soil，K2O 0.22 g/kg soil.The value of SPAD in the fruit enlargement period decreased apparently when fertilization amount was N 2.0 g/kg soil，K2O 2.2 g/kg soil.POD activity in the leaves increased with the increase of fertilizer application，but the root activity was contrary and decreased obviously when fertilizer amount was N 0.8 g/kg soil，K2O 0.88 g/kg soil.The content of malondialdehyde (MDA) appeared an increasing trend.When the fertilization amount was N 1.6 g/kg soil，K2O 1.76 g/kg soil，chloroplast grana lamellae was getting to be not obvious，stroma lamellae became to be fuzzy，and osmiophilic particles increased.The cavity appeared in the mitochondrial inner，ridge structure became fuzzy，plasmolysis was obvious.In a word，plants could grow normally with fertilization amount of N 0.8 g/kg soil，K2O 0.88 g/kg soil，and when fertilization amount was more than N 1.6 g/kg soil，K2O 1.76 g/kg soil，plant couldnt grow well.