The moisture transfering in air over northwest arid area was analyzed in this paper The results show that: (1) on an average, the maximum moisture transfering is at 600 700 hPa, but a few are near the ground for local effect in this area (2) The moisture transfering in summer is twice that in winter in this area (3) The loss of moisture in air in this region is supplied by evaporation of surface run off flowing in this region.