Abstract: Gasilla tomatoes grown under film drip irrigation in solar greenhouse were used as research objects.Four irrigation control experiments were carried out.Root growth and tomato fruit were sampled in the experiment, and the yield, water use efficiency and main quality factors of tomato were comprehensively analyzed by principal component analysis.The effects of different irrigation levels on growth physiological parameters, yield and quality of tomato were studied, in order to find the optimal irrigation system under mulched drip irrigation.The results showed that water uptake depth of tomato roots ranged from 0 cm to 60 cm.With the decreases of irrigation amount, root length, root surface area, and root volume decreased.The water consumption, yield, and WUE of tomato under full irrigation during the whole growth period of spring and autumn were 297.56 mm, 5.42 t·hm^-2,15.59 kg·m^-3 and 230.65 mm, 2.97 t·hm^-2,8.77 kg·m^-3,respectively.With the decreasing of irrigation amount, WUE and quality increased, while yield decreased.Considering the yield, WUE and main quality factors of tomato, the optimal irrigation amount of drip irrigation under film was 55% ET₀ in solar greenhouse.