The experiment included four levels of the soil water deficit (threshold of soil water potential before irrigation) applied in the middle period of fragrant pear growth: slight (-100kPa), moderate (-200kPa),severe (-300kPa) water stress and the control (-50kPa). The irrigation system was surface drip irrigation. The results indicated that the water stress irrigation significantly reduced the summer pruning weight, improved the yield. Under full irrigation, the root length density (RLD) decreased with the increment of distance from the tree row, and root development in the wetted zone of drip irrigated pear tree was enhanced. The RLD at 0.5m from the tree row decreased with the depth; however, the RLD in the range from 1m to 1.5m from the tree row increased with the depth; in the non-irrigated zone at 2m from the tree row, the differences of RLD among the depths were not obvious. The RLD in the wetted and non-irrigated zone adjusted significantly due to the water stress in the wetted zone, as compared to the control. Increase of RLD due to the moderate soil water deficit showed some positive effects to the yield improvement.