The invention discloses a measurement device for detecting the porosity of saturated soil and an application method of the device. The measurement device comprises a cutting ring, a stainless steel electrode, a cutting ring, an organic glass box and an impedance tester. When the impedance of a soil sample is measured, the cutting ring is selected according to the property of the soil sample; the stainless steel electrode is connected with the impedance tester through a connecting wire; when the impedance of pore water is measured, the organic glass box is selected and the stainless steel electrode is connected with the impedance tester through the connecting wire; and a frequency selector and an electric level adjuster are connected with a computer through the impedance tester. The device disclosed by the invention can be used for collecting the soil sample, preparing the saturated soil sample, setting electric signal frequency and impedance testing voltage and determining the resistivity of the saturated soil and pore water; and soil properties and cementation factors are selected according to the property of the soil sample and the porosity is obtained by the computer. The measurement device disclosed by the invention has the characteristics of simplicity and feasibility, low cost, short measurement period, accurate result and the like; expensive equipment is not needed and an operation method is simple; and the measurement device can be operated in a laboratory or a filed and the practical applicability is very high.