The effect of potassium(K)fertilizer on tomato growth and calcium(Ca)and magnesium(Mg)uptake was studied to provide theoretical and technical basis for balanced fertilization of vegetables under the facility condition.A pot cultivate experiment was conducted with the treatments of one control(CK)and five K fertilizer levels(150，300，450，600 and 750 kg/hm²，which were represented by T1，T2，T3，T4 and T5，respectively)using tomato as testing crop.The result showed that:1)With the increase of K application，the number of healthy root tips increased significantly，the root total area and the number of branches had an increasing tendency.2)Comparing with CK，the plant height increased by 15.8% and the biomass of root，stem and leaf increased significantly after applying potassium fertilizer，which increased by 56.8%，27.1% and 33.2%，respectively，for the T5 treatment.3)With the increase of K application，the yield was increased，which was increased by 15.11% in T5 compared with CK.4)With the increase of K application，the concentration of K and Mg in roots，stems and leaves increased significantly，but the concentration of K and Mg in fruits decreased significantly.With the increase of K application，the concentration of Ca in roots and stems and leaves and fruits decreased significantly.In conclusion，applying K fertilizer improved the biomass and yield of tomato significantly，and increased the K and Mg uptake in different organs of tomato，but it would inhibit Ca uptake，and the transport of K and Ca and Mg were inhibited by K fertilizer.