In order to explore the effective way to improve the water use efficiency of tomato in the sunlight greenhouse, the effects of lateral depths on growth, fruit shape and quality of tomato under different water deficit were studied through drip irrigation experiment in 2014 and 2015. Results showed that lateral depth had a significant influence on yield, irrigation amount (p＜0.05), and had no significant impact on irrigation water use efficiency and quality (p＞0.05). The growth rate of tomato was faster and fruit diameter was bigger when lateral was buried at 20cm depth. Under moderate and moderate-mild water deficit, lateral buried at 20cm depth could significantly decrease the fruit ratio of C grade (fruit diameter D＜6.5cm) by 29.2%, and increase the fruit ratio of A grade (D≥7.5cm) and B grade (6.5cm≤D＜7.5cm) by 16.6% and 2.0%, respectively. The changing trend of yield and irrigation amount of tomato showed a first increase and then decrease trend with the increase of lateral depth, the value of yield for lateral depth buried at 20cm was the highest (66.44t/hm2). Yield and irrigation water use efficiency of tomato were decreased significantly with the increase of irrigation threshold (p＜0.01), so irrigation amount can be reduced while the yield and water use efficiency of tomato can be increased by adopting different combinations of lateral depth and irrigation threshold. Therefore, lateral depth of 20cm and irrigation threshold of 60% of field capacity would be the most appropriate treatment combination for tomato cultivation in the sunlight greenhouse in Guanzhong region of Shaanxi Province. For the observed responses, the information on how the tomato adapted to different lateral depths under water deficit condition would provide guidance for field production practices as well as indications of possible mechanisms.