Field experiment was conducted to evaluate the effects of regulated deficit irrigation on the fine roots redistribution of mature Korla fragrant pear trees planted in the oasis in 2009 and 2010. The experiment consisted of drip and flood irrigation plots. The drip irrigation plots included two water deficit treatments: applying 60% (moderate) and 40% (severe) of pan evaporation during the slow growth stage of both shoot and fruit (stage 2), and 80% (full irrigation) of pan evaporation in the two other stages, and the control treatment: applying 80% of pan evaporation during the whole growth season. The flood irrigation plots were irrigated with amount of 300mm per month from April to August. All the experimental plots were flood irrigated before 2009. The results showed that fine roots of mature Korla fragrant pear trees mainly distributed in 20~60cm soil layers. The previously flood irrigated Korla fragrant pear trees spent two years on adapting to the irrigation mode transformation from flood irrigation to drip irrigation through redistributing their fine roots. Water stresses decreased fine roots length and inhibited the vegetative growth of fragrant pear trees, while the resumption of full irrigation boosted their growth. The water deficit inhibited fine roots development more effectively than shoots, owing to the near cessation of shoot growth in stage 2. However, no remarkable correlations between fine roots length and fruit yield were observed. The results provided the theoretical basics for regulated deficit irrigation application to the mature fruit trees planted in the extremely arid regions.