Abstract: Based on the water culture，the different levels of K (0.0，4.0，8.0 and 16.0 mmol/L)，different potash fertilizers (KNO3 and K2SO4) and two tomato cultivars (ZZ106 and MF802) were selected to study the effects of potassium on seedling growth and phenol metabolism of tomato．The results show that the contents of secondary protective enzyme activities and secondary substances of the leaves and roots in the treatment of (8.0 mmol/L) are higher than those of other treatments．The biomasses and contents of K of the plants in the treatments of K2SO4 are higher than those in the treatments of KNO3, while the PAL activities, total phenol, flavonoids and lignin contents in the treatments of K2SO4 are lower than those of KNO3．The secondary protective enzyme activities and secondary substances, biomasses and K contents of leaves of the ZZ106 are significantly higher than those of the MF802, while the K contents of roots of the ZZ106 are significantly lower than those of the MF802．In short，K in leaves and roots can improve phenol metabolism．The potassium deficiency and over dose can reduce the metabolism of the enzyme activity and contents of phenolic，flavonoids and lignin．K2SO4 can promote tomato plant growth, but KNO3 is an advantage over K2SO4 on phenol metabolism．The growth and phenolic compounds of the ZZ106 are better than those of the MF802.