Abstract: Drip irrigation under mulch is an efficient and water-saving irrigation practice implemented in the arid agricultural areas of China. Based on the micro environments specific to drip irrigation, i.e. "middle of the film", "between the film", "edge of the film" and "outside the film", as well as the 5 960 data collected during 2011—2013 by field contrast test, the relationships between soil level environment, irrigation quota, soil moisture, temperature, evaporation and water-salt movement were established through the Cobb-Douglas model. The results showed that, in arid irrigation areas with strong evaporation and under the combination of plastic film mulching and drip irrigation, soil water and salt migrate horizontally from the "middle of the film" towards the exposed "edge of the film", and vertically from the lower to the upper soil layers, tending to accumulate in the boundary at the "edge of the film". The interaction between temperature and evaporation, especially, drives the movement of soil water and salt at mulching spaces and in bare soils. The research further revealed the directional migration of soil water and salt in the context of drip irrigation under mulch, and can provide a basis for the application of water-salt surface discharge method in soils.