Objective To investigate the relationship between hepatic venous outflow obstruction (HVOO) and patterns of the hepatic vein (HV) drainage into inferior vena cava (IVC) in piggyback liver transplantation (PBLT).Methods A retrospective analysis on 202 cases of PBLT (from May 2000 to Aug.2015) was conducted.The recipients' patterns of HV drainage into WC and the angle ∠COB between the reconstructed outflow and IVC in the cross section were recorded by preoperative 3D reconstruction.And the lengths and diameters of recipients' HVs were measured during operations.The relationship between the incidence of HVOO and patterns of HV drainage into IVC was analyzed.Results There were 3 patterns of HV drainage into IVC:type Ⅰ (n =136),trunk of left and middle HVs;type Ⅱ (n=52),trunk of right and middle HVs;type Ⅲ (n=14):trunk of three HVs.There was no statistically significant difference within the HVs of each type,when the lengths and diameters were compared respectively.However,the angle ∠COB of type Ⅰ [(164 ±10.14)°] was significantly bigger than type Ⅱ [(44 ± 12.2)°] and type Ⅲ [(96 ± 13.1) °] (P＜0.05).Accordingly,the highest incidence of HVOO (23.5％) was foundin type Ⅰ,followed by type Ⅱ (9.6％),and type Ⅲ had the lowest incidence (7.1 ％) (P＜0.05).The correlation coefficient Cramer's V =0.765.Conclusion This study demonstrated that there was preferable relativity between the HVOO incidence and the patterns of HV drainage into IVC.Type I is more likely to have HVOO.Type Ⅲ is the most ideal one for PBLT.