The invention discloses a calculation method for saturated-clay frost heaving ratio in a closed system. The method comprises getting soil from an on-site clay layer, obtaining the standard soil sample mass and the residual soil mass at a natural state through an indoor geotechnical test, measuring the residual soil particle mass by utilizing a drying process, and measuring the relative density by utilizing a pycnometer process, so as to obtain the water content and the soil-particle relative density of the soil sample; saturating the soil sample by utilizing a vacuumizing process, measuring the mass of the saturated soil sample, and calculating the saturation water content; and calculating the soil-particle volume and water volume in soil according to the soil-sample total volume, and the soil-particle density and the water content, establishing a calculation formula of the saturated-clay frost heaving ratio related to the saturation water content and the soil-particle relative density in the closed system. The beneficial effects comprise that the method fills the blank for calculating the clay volume expansion in the closed system in the artificial freezing field, establishes a function formula employing the saturation water content and the soil-particle relative density as independent variables, and is capable of relatively effectively determining the saturated-clay frost heaving ratio in a closed environment.