Abstract: To study the time-dependent deformation characteristics of high-fill subgrade in mountainous areas, the water-retention characteristics of coarse filler and a series of rate-dependent mechanical properties tests under constant suction are carried out for the coarse filler of subgrade. Three different shear rates are used to shear the samples, and the effects of confining pressure, matrix suction and shear rate on the strength and deformation characteristics of soil are analyzed. The test results show that there is no residual suction value in the soil-water characteristic curve of coarse filler. The peak strength of coarse-grained fill under different confining pressures can be expressed as a function of matrix suction. The greater the matrix suction, the higher the shear strength of unsaturated coarse-grained soil, and the smaller the volume shear deformation. The strength and volume deformation of unsaturated coarse-grained soil are affected by the shear rate, and the change trend shows high consistency. The higher the shear rate, the higher the sample strength, and the smaller the corresponding volume deformation.