In-situ remediation technology has become the mainstream of contaminated site management， but in-situ remediation technology is prone to slurry return， resulting in secondary contamination of the soil. In this paper， we designed a packer for in-situ remediation of contaminated sites using the principle of hydraulic expansion and elastic contraction， which can meet the requirements of the rotary injection process and enable the recycling of the packer. A model of the action mechanism of the packer was developed using FLAC3D， and the radial stress and displacement of the soil layer under different input pressures were analyzed at the microscopic level. The simulation results showed that the effect of the packer on the cohesive soil layer is in the range of about 1.5m. This study provided a reasonable reference for the optimization of in-situ remediation techniques for contaminated sites.