Abstract: Under sand culture, after fruit setting of the first truss, the effect of K/N ratio of nutrient solution on plant growth, fruit quality, yield and nutrient content of tomato were investigated. The results showed that it can promote plants’ nutritional growth, improve fruit quality and production, balance nutrients’ assimilation and distribution of plants when the K/N ratio of nutrient solution was increased in the fruit-set period, but if the K/N ratio was too high it will inhibit the promoting effects. T4 treatment (K∶N=2.5∶1)could improve the content of chlorophyll significantly, the photosynthetic capacity could be improved too, and fruit qualities could also be improved significantly, but at the same time it markedly increased the incidence of blossom-rot fruits. T3 treatment (K∶N=2.1∶1)could get the maximum total fruit number and the highest yield per plant, and fruit quality was better. The root-shoot ratio and the content of dry matters of plant roots, stems, leaves in this treatment were also the highest. The content of K in roots, stems, leaves in T3 treatment were in the middle, and the assimilation and distribution of N and P ranked only second to T2 treatment. Considering nutritional growth, fruit quality, yield and so on, T3 treatment (K∶N=2.1∶1) was the optimal K/N ratio in the fruit-set period of tomato under sand culture.

Key words: sand culture, tomato, K/N ratio, fruit-set period