Abstract: The flat dilatometer test (DMT) has been widely used in engineering such as geotechnical engineering investigation and evaluation of ground improvement effect at home and abroad. The test process of DMT is usually carried out after the blade insertion of DMT into test position, so the disturbance caused by the dilatometer penetration process will directly affect test results to a certain extent. However, the mechanism of dilatometer penetration and soil disturbance and its influence on test results caused by penetration process are not yet known. Homogeneous dry sand samples under different initial densities are prepared by the layered plate compaction method with low level rainfall, and several laboratory model tests of dilatometer penetration into these sand samples together with particle image velocimetry (PIV) are carried out to investigate the distribution characteristics of the soil displacement field during the blade penetration process. The test results show that (1) the extrusion effect caused by the penetration of both the wedge part and lateral expansion part of the blade mainly causes soil disturbance. (2) The surrounding soil is squeezed downward and sideward during the penetration of the wedge part of blade, resulting in small vertical displacement and a flat displacement field which mainly extends to both sides, while the surrounding soil is squeezed horizontally to the two sides during the penetration of the lateral expansion part of blade, resulting in a semi-elliptical horizontal displacement field with the distribution range being obviously larger, and meanwhile, the shear effect caused by side friction between the blade and soil produce a vertical displacement field with a narrow range. (3) Moreover, the displacement field of dry sand caused by dilatometer blade penetration is less affected by the initial sand density than that by cone probe penetration, and only the distribution range of displacement field around the wedge part of the dilatometer blade expands with the increase of the initial density to some extent.