Abstract: Saline alkali wasteland and low-yield fields are important reserve of cultivated land in China. The chemical methods of industrial waste desulphurization gypsum (CaSO4·2H2O) have achieved certain results and good environmental protection benefits at the aspect of improving alkaline soil. Scarce water resource, soil hardening and salt concentration in early improvement are still the key factors that restrict the development of agricultural production in chapped alkali soil by using waste desulfurization gypsum from power plant. In order to improve rainfall utilization efficiency, and restrain the problems of salt aggregation on soil surface and soil compaction in the process of chemical improvement of alkaline soil, a field experiment was conducted, which included 3 soil surface mulching methods: combined mulching of plastic film and straw (the straw was firstly used, then covered with mulching film, and later seeding was conducted artificially; the aperture was 4 cm, and the straw mulch was restored at the orifice after sowing), plastic film mulching (white transparent polyethylene film, width of 2 m, thickness of 0.02 mm), and straw mulching (spring wheat straw, length of 8-12 cm, coverage amount of 0.6 kg/m2). The experiment included 4 treatments: plastic film and straw combined mulching (PSM), plastic film mulching (PM), straw mulching (SM) and conventional tillage (CK), which were designed to explore the dynamic structure characteristics of soil water salt and its effect on yield of oil sunflower (Helianthus annuus) at Pingluo saline-soil Experimental Station in Ningxia. The soil moisture contents at the depth of 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 cm were measured; soil salt contents and soil bulk densities of different soil depth profiles (10, 20, 30, 40, 50, 60 cm) were measured for different treatments. And the results showed that: The PSM treatment effectively improved the water storage and water holding capacity of 30-100 cm soil layer. It delayed the time of oil sunflower consuming the moisture in 60-100 cm soil depth. The water activity in the 30-90 cm soil layer under PSM treatment was higher than that of other single coverage models. Salt accumulation on soil surface was delayed to the later stage of crop growth, and its level was significantly lower than the other 3 treatments, reducing the toxicity of soil salinity in early salt-sensitive growth period of crops compared with single coverage and conventional planting. The combined mulch promoted the improvement of soil structure with relatively low soil bulk density and higher soil porosity, which is beneficial to improve soil effective water storage capacity and accelerate the process of leaching. The PSM treatment improved survival rate and yield of oil sunflower in seedling stage. The precipitation use efficiency under the PSM treatment was increased by 14.71%, 86.45% and 59.05% respectively compared with the PM, SM and CK treatments, and the water use efficiency was increased by 10.80% and 32.71%, respectively, compared with the SM and CK treatments. Therefore, the plastic film and straw combined mulch can improve soil structure, which is beneficial to enhance soil effective water storage capacity and accelerate the process of leaching.