Abstract: In order to promote the application and promotion of soybean straw-based water retaining agent (WRA) in agriculture, effects of WRA rate on soil physical prorerties and tobacco growth were studied by the field experiment in dry area of Nanyang, Henan province. The results showed that water loss was reduced by WRA obviously with its application amount, and the WRA improved soil physical properties, increased the porosity in soil and decreased soil bulk density. WRA application enhanced the total soil porosity, especially non-capillary porosity, and consequently improved the soil aeration condition. However, excessive application of WRA reduced non-capillary porosity, leading to soil compaction. Furthermore, the application of WRA decreased transpiration rate of tobacco, improved leaf photosynthetic characteristics and water use efficiency, and strengthened drought resistance of tobacco. It also enhanced the plant height, stem thickness and maximum leaf area of tobacco, and improved the tobacco quality. The average moisture content of soil, total soil porosity, yield and the proportion of superior tobacco increased by 3.1%, 6.8%, 18.4% and 6.8% respectively when the suitable application rate of WRA was 240 kg/hm2.