Abstract: In recent years, the unloading of excavation engineering activities such as foundation pits and tunnels has caused excessive lateral deformation of cohesive soil, which result in more and more engineering accidents. At present, the inclinometer is often used to monitor the horizontal displacement of the soil around the foundation pit. However, due to the special engineering properties of soft soil, the inclinometer cannot be driven to deform with the soft soil during monitoring. The effect of monitoring is often unsatisfactory and inaccurate to reflect the true deformation. Therefore, it is necessary to strengthen the research of lateral deformation monitoring technology of soil in the construction of excavation unloading engineering. In this paper, based on the directional characteristics of the deformation of magnetic minerals under loading, the magnetic fabric test is used to study the magnetic anisotropy of the cohesive soil sample after unconfined compression test and then to compare with the results of the confined one. The paper then discusses the mathematical relationship between the main magnetic susceptibility value and the strain as the consequence of the analysis of the influence of the axial stress and the moisture content of soil on the magnetic anisotropy under unconfined compression. Finally, the feasibility of the calculation of the law of force and the deformation from the magnetic anisotropy of the cohesive soil is explored. The research results show that the deformation of the cohesive soil under force has good consistency with its orientation of magnetic mineral. This understanding has important theoretical significance and practical application value for effectively monitoring the deformation of soft soil around unloading projects in soft soil areas.