Objective To investigate the influence from compressing manipulation by flexing hip and knee in supine position on stress distributions in the pelvis and strain distributions in the sacroiliac joints by 3D finite element method, and discuss the possibility of moving the whole sacroiliac joints under such manipulation. Methods A 3D finite element model of the normal pelvis was constructed based on CT images. According to the manipulation principle, the compressing force in flexing hip and knee was decomposed in two directions, and loaded on the 3D finite element model to calculate stress of the pelvis and strain of the sacroiliac joints. Results Under the loading of simulative manipulation, stress of the pelvis was mainly located at 1/3 part of the anterior inferior of the sacroiliac joints, the greater sciatic notch, and the middle 1/3 part of the inferior and anterior of gluteal lines. The maximum strain of the sacroiliac joints was mainly located in the posterior superior, posterior inferior and central 1/2 part of the sacroiliac joints. Conclusions The compressing manipulation by flexing hip and knee can only move 1/3 part of the interior of the sacroiliac joints, rather than the whole of the sacroiliac joints.