Abstract: Abstract: Drip irrigation is being effectively used for alfalfa production in arid northwest China. The objectives of this paper were: i) to compare the effects of flood and drip irrigation on the spatial distribution of water and salt; ii) to compare effects of biomass, spatial distribution and dynamics of fine roots of alfalfa on the movement of water and salt in the soil profile under flood and drip irrigation. From May to October 2012, the plot experiments were carried out in Xinjiang Province. Flood irrigation (irrigation quantity is 4 600 m3/hm2) and drip irrigation treatments were set up (irrigation quantity is 4 200 m3/hm2), alfalfa planted in wide-narrow row plantation with a distance of 15 cm + 30 cm + 15 cm between rows. The results showed that soil water in the flood irrigation treatment was concentrated in the upper 15 cm of the soil profile. Furthermore, the soil water content was uniformly distributed across the plots, ranging between 19.5% and 20.5%. In the drip irrigation plots, soil moisture was concentrated in the upper 40 cm of the soil profile and within 30 cm on either side of the emitter of drip irrigation tapes, and the soil water content ranged between 18.0% and 20.0%. Flood irrigation leached salt to below the 30 cm depth. As a result, salinity in the 0-30 cm depth decreased from 0.4-0.5 mS/cm to 0.3 mS/cm or less. Drip irrigation significantly reduced the salinity to 0.2 mS/cm in the root zone. The narrower-deeper-type soil wetting pattern and desalted zone were formed in drip irrigation and alfalfa planted in this area has higher water content and lower salt content than flood irrigation, therefore drip irrigation provides excellent soil environment for alfalfa growth. While wider-shallower-type soil wetting pattern and desalted zone were formed in flood irrigation. Compared with the flood irrigation treatment, fine roots in the drip irrigation treatment were concentrated in the 0-50 cm depth and near to the emitter of drip irrigation tapes. Total fine roots biomass was greater in the drip irrigation treatment (212 g/m2) than that in the flood irrigation treatment (198 g/m2). Fine root biomass fluctuated during the growing season because of regrowth of alfalfa and harvest schedule. Fine root biomass ranged from 193 to 244 g/m2 in the drip irrigation treatment and from 183 g/m2 to 219 g/m2 in the flood irrigation treatment. During the entire growing period, live fine root biomass was greater in the drip irrigation treatment than that in the flood irrigation treatment. Live fine root biomass was fluctuated in flood and drip irrigation obviously, ranged from 73 to 139 g/m2 and 97 to 144 g/m2 respectively, During the early growth stages (from 2nd April to 18th July), the biomass of dead fine roots changed more smoothly in the drip irrigation treatment (ranged from 93 to 101 g/m2) than in the flood irrigation treatment(ranged from 96 to 125 g/m2), but the biomass of dead fine roots in drip irrigation was fluctuated from 72 to 102 g/m2 after 18th July. Biomasses of live and dead fine roots both changed continuously because of rapid turnover of fine roots, first increasing (growth), then decreasing (death and decomposition), and then increasing again (regrowth) . The results indicated that drip irrigation provide suitable soil condition for alfalfa growth by redistribution of soil water and salt, and the model of the wide-narrow row plantation with a distance of 15 cm + 30 cm + 15 cm between rows and drip irrigation is the optimal cultivation pattern of alfalfa.