Objective To investigate the influence of venous drainage position on the direction of arterial blood flow in the conjoined flap. Methods Seventy-two Sprague-Dawley rats were randomly divided into four groups: normal group received no treatment; the control group only remained the right intercostal posterior artery and vein; experimental group 1 only remained the right intercostal posterior artery and the left intercostal posterior vein, and experimental group 2 only remained the right intercostal posterior artery and the left iliolumbar vein. The distance among the angiosomes was measured. At day 7 after surgery, the survival rate of the flap was measured and the morphology of vessels by lead oxide-gelatin angiography was observed. Materials from the choke-area 1 was drawn, HE staining was used to compare the diameter expansion of the artery. Blood from the tail vein was collected, and the contents of lactate was detected. Results The distance of angiosomeⅠtoⅡ was nearest, Ⅰ to Ⅲ was farthest, the difference was statistically significant (P<0.05). At day 7 after surgery, the survival rate of the control group was (86.5±4.3) percent, while 100 percent in experimental groups 1 and 2. Angiography showed that the number of blood vessels was relatively small in control group, larger in experimental group 1, and the largest in experimental group 2 in regions of angiosome Ⅲ and Ⅳ. Compared to the normal group, the diameter of the artery of the experimental 2 was most obviously expanded, followed by the experimental group 1, the difference was statistically significant (P<0.05). The lactate contents in the control group was the highest, the difference was statistically significant (P<0.05). Conclusion Changes in position of venous drainage can result in the changes of the effect of arterial perfusion and venous drainage, and then alter the vascular rete, improve the flap survival.