Objective To investigate the changs of Choke veins for cross-area flap at the dorsum of the rat. Methods Firstly, the vessels distribution of 30 SD rats was studied by lead oxide-gelatin one-time whole vascular perfusion technique. Secondly, a cross-area flap at the size of 10.0cm×3.5cm was cut out at either side of dorsum in 10 SD rats and placed in the skin window. The changes of Choke vessels were observed and photographed for 8 days under the stereomicroscope. The skin windows were placed in another 2 SD rats before 2% Evans blue was injected about 1 ml in each rat by tail vein and the microcirculation of choke vessels was recorded by video. Results After the cross-area flap was cut out, the vascular diameter dilated in both choke artery and veins. However, the most obvious dilation was found in the connection venules. The dilation of connection venules began at the (60±12)th hour after operation and continued till (4.5±0.5) days. The whole circulation process was observed in the Choke vessels by Evans blue injection in tail vein and the blood velocity at the choke artery was approximately 2.53mm/s. Conclusion In the earlier stage following the flap cutting out, the backflow of venous blood gives priority to the labyrinth type, while the backflow of venous blood is valve failure in preference to the labyrinth type at the later stage. Evans blue as a blood tracer is suitable for the blood blow dynamics research in the microcirculation of skin flap when combining with the direct observation of skin window.