The invention provides a soil body one-way strain testing device. The soil body one-way strain testing device is buried into a soil body and is connected with a data acquisition system; the device comprises a rigid pipe, an elastic bag, a pressure sensor, filling liquid, a data line, a sealing ring, a sealant and a hole plug, wherein a round hole and a liquid filling hole are formed in a side wall of the rigid pipe; sealing grooves are formed in outer walls at two ends of the rigid pipe; a testing end of the pressure sensor is put into the rigid pipe through the round hole in the side wall of the rigid pipe; the sealing ring is used for arranging the elastic bag onto the sealing grooves of the rigid pipe; the filling liquid is filled into the rigid pipe from the liquid filling hole and the liquid filling hole is sealed by the hole plug; a seam on the rigid pipe is filled and compacted by utilizing the sealant; the data line connected with the pressure sensor is connected with the data acquisition system so as to form the soil body one-way strain testing device. Meanwhile, the invention provides an implementation method of the soil body one-way strain testing device. The strain amount of the soil body under the action of an external load can be obtained; the device provides convenience for knowing mechanical and deformation properties of the soil body.