Objective: This study aims at exploring the relationship between the establishment of collateral circulation caused by iliac vein compression (IVCS) and the deep venous thrombosis (DVT). Methods: Different types of ideal collateral circulation models and IVCS patient-specific models were numerically simulated using computational fluid dynamics (CFD) in combination with the blood stasis model. The relationship between blood retention and collateral types and cross-sectional area was studied, and the relationship with thrombosis was explored. Results: Wall shear stress (WSS) of the distal end part of each ideal model was about 0.3Pa. After four cardiac cycles, the residual blood stayed at the stenosis and the distal end part for the lumbar ascending and pelvic type models, the old blood volume fraction (OBVF) varied with collateral cross-sectional areas, ranging from 5-90% and 70-80% respectively. The OBVF of the coexistence model was above 80%. The WSS at the distal end part of the patient-specific model was 0.9Pa, and the OBVF at the distal end part was 51.5%. Conclusion: The stenosis and the distal end part are most prone to blood stasis, and closely related with DVT. The larger the cross-sectional area of the collateral, the more serious the blood stagnation; blood stagnation of the coexistence model is higher than the lumbar ascending type and pelvic type.