Abstract: A series of laboratory tests are conducted on sandy loess taken from Yangcheng Tunnel of Haoji Railway under different dry densities by the combination of tensiometer method, filter paper method, and dew point hydro potential meter (WP4C) method. The soil-water characteristic curve (SWCC) of sandy loess in a wide suction range is obtained, and the effect of the initial dry density is emphatically studied. The van Genuchten model is used to fit the SWCC test results under different dry densities and the air entry value of the SWCC is determined. The microscopic pore structure of sandy loess with different dry densities and water contents is studied by scanning electron microscope tests. The change rules of the initial saturated water content, water loss rate and air entry value of SWCC under different dry densities are observated from a macro-micro perspective. The test results show that the volumetric water content of sandy loess decreases with the increase of matric suction, and the pore structure of soil changes from more overhead pores to more uniform medium pores with the increase of dry density. The initial saturated water content and water loss rate gradually decrease, and the air entry value gradually increases.