The invention relates to a sample micro motion detecting device for a large-scale structure experiment, comprising a displacement sensor which comprises a main part and a magnetic loop part, wherein, a sample and the main part of the displacement sensor are fixedly connected with a linear guide rail; the magnetic loop part of the displacement sensor is fixedly connected with a sliding block matched with the linear guide rail; and the motion direction of the sliding block is parallel to the displacement direction of the sample. Because the adoption of the device for combining the guide rail and the sliding block, so that small displacement in the horizontal direction of the tested sample can be smoothly detected through the sample micro motion detecting device during testing, even under high loading condition of receiving tension-compression test force Fv (maximum reaching 10000kN) applied by the vertical loading actuator.