The invention provides a method for determining unfrozen water content of frozen soil through measuring electrical resistivity. The method comprises the following steps: preparing a cylindrical saturated soil sample by utilizing a PVC (Polyvinyl Chloride) plastic pipe; respectively determining the volumes of soil particles and pore water in the saturated soil sample; determining cross sectional areas of the soil particles and the pore water in the saturated soil sample; freezing the saturated soil sample in a low-temperature test box, uniformly smearing the upper and lower circular surfaces of the cylindrical saturated soil sample, and measuring the resistance of the cylindrical saturated soil sample by using a multi-meter; calculating the electrical resistivity of the saturated soil sample at each temperature; drying the determined saturated soil sample in a drying box, determining the resistance of the dried saturated sample soil, and calculating the electrical resistivity of the dried saturated soil sample; calculating the volume of the unfrozen water of the saturated soil sample until the unfrozen water content is calculated. The method has the beneficial effects that the unfrozen water content of the frozen soil at different negative temperatures can be obtained; a calculating result is accurate and reliable; the measurement error of the method is within 2.4 percent; the test accuracy of the unfrozen water of the frozen soil is ensured; convenience can be provided for temperature field calculation in frozen soil engineering construction.