Objective To explore the prone site of pressure injuries in buttock in sitting position and the biomechanical response of different soft tissues, so as to provide references for effective prevention of deep tissue pressure injury. Methods Based on CT scan data of the buttock, the finite element model of the buttock in sitting position was established, including the bone, muscle, fat, skin tissues and cushion model. Tissue injury was simulated using life-death elements. The pressure measurement data of the experimental cushion interface were compared with the finite element simulation results to verify validity of the model. The mechanical state of the sitting position was simulated, the stress and strain of soft tissues were studied, and the compressive stress in different soft tissues and the possible damage after exceeding the limit values were analyzed. Results By comparing the simulation results of the cushion model with the experimental interface pressure measurement results, the model was proved to be effective. Stress concentration occurred in soft tissues below the ischial tuberosity in sitting position. The peak transverse compressive stress and peak shear stress in gluteus maximus were 38 kPa and 3. 4 MPa, respectively. The maximum compressive stress and peak shear stress in adipose tissues were 22 kPa and 4. 5 MPa, respectively, which did not appear directly below the ischial tuberosity. Conclusions Deep tissue injury may occur when soft tissues are subjected to a certain magnitude of pressure load within a certain time period. When the sitting position is maintained for a certain period of time, the position