Soil moisture plays a key role in determining tomato growth, yield, and quality. Soil moisture directly or indirectly affects the growth and distribution of the root system. Under soil moisture stress, plant water and nutrient uptake depend on root size, morphology, and competition. It is important to study tomato root growth under different soil moisture treatments to optimize water and nutrient utilization efficiency. Previous studies have mostly investigated the physiological and biological effects of soil moisture on tomato fruit, and many studies have discussed certain aspects of individual mechanisms. In this study, the growth of both roots and all above-ground parts of tomato plants under each moisture treatment was observed. Soil moisture data were combined with whole plant growth status to reveal dynamic changes in tomato roots and above-grounds part in response to soil moisture stress.We used the tomato (Lycopersicon esculentum) cultivar ‘Jingfen 2’ in our experiment, which was performed in a controlled environment greenhouse at the Nanjing University of Information Science and Technology from May to August of 2013. Four soil moisture treatments were applied:normal water supply (T1), mild water stress (T2), moderate water stress (T3), and severe water stress (T4). The growth of roots and above-ground parts of tomato plants were observed. Among the four soil moisture treatments, measurements of four root growth parameters (total root length, total root surface area, average root diameter, and number of root tips) were in the following descending order:T2 > T3 > T1 > T4. Maximum total root length in T2, T3, and T4 was 1.8-, 1.0-, and 0.4-fold that of T1, respectively. Total root surface area in T2, T3, and T4 was 2.3-, 1.1-, and 0.4-fold that of T1, respectively. Average root diameter in T2, T3, and T4 was 1.3-, 1.1-, and 0.6-fold that of T1, respectively. Root tip number in T2, T3, and T4 was 1.1-, 1.0-, and 0.5-fold that of T1, respectively. In T1, T2, and T3, tomato roots were distributed mainly in the 5-10 cm soil layer, but in T4 most roots were in the 15-25 cm layer. Plant height, stem diameter, and leaf area index (LAI) of tomato plants decreased with increasing soil moisture stress. Compared with T1, plant height in T2, T3, and T4 was reduced by 11.49%, 28.60%, and 43.98%, respectively. The minimum stem diameter was found in T4, which was 73.57% of the tomato stem diameter in T1. LAI differed significantly (P < 0.05) among soil moisture treatments; LAI in T2, T3, and T4 was 81.33%, 64.62%, and 43.37%, respectively, of that in T1. Soil moisture was positively correlated with growth indices of root and above-ground parts, and soil moisture content in the 20-cm layer had the highest correlation with root growth indices. The mild water stress treatment (T2) did not significantly affect the growth of above-ground parts, while it benefited root growth. The moderate and severe water stress treatments (T3 and T4) significantly inhibited the growth of above-ground parts and decreased the extent of root distribution in the soil. The results of this study may provide a scientific basis for water management in greenhouse tomato production.