Objective A simplified pelvic model of a patient was established, and periacetabular osteotomy (PAO) was simulated to investigate its effects on the stress in the sacroiliac joints in the standing position. Methods The anterior center edge angle (ACEA) and lateral center edge angle (LCEA) of the patient’s hip model were adjusted, and 27 postoperative models were obtained. Finite element calculations and analyses of each model were performed during single-leg standing and double-leg standing. Furthermore, an investigation of the stress variations and distributions on the sacroiliac cartilage was conducted in combination with a hip joint stress analysis. Results During single-leg standing, the maximum stress on the sacroiliac cartilage of a healthy individual was 18.2 MPa. With an increase in the anterior center edge angle (ACEA), the von Mises stress of the sacroiliac cartilage decreased from 34.5 MPa to 19.8 MPa. The maximum von Mises stress in the acetabular cartilage decreased from 4.767 MPa to 2.7 MPa. Before the ACEA attained 36°, the maximum von Mises stress exhibited a downward trend. After it attained 36°, the stress distribution began to increase, and the stress distribution improved significantly. During double-leg standing, the minimum and maximum von Mises stresses on the sacroiliac cartilage of the affected leg side was 2.8 and 6.5 MPa, respectively. The sacroiliac cartilage stress on the normal leg side did not vary significantly, and the stress difference between the two leg sides decreased gradually. Conclusions PAO can improve the hip joint stress and sacroiliac joint stress. Additionally, the improvement of sacroiliac joint stress is identical to that of hip joint stress. Prior to surgery, a comprehensive planning of the hip and sacroiliac joints can be used as a reference by doctors. This is of high significance for patients with developmental dysplasia of the hip (DDH) to achieve better outcomes.