The key points for observing the blood supply of free flaps after microsurgery include: ① Regularly position and measure skin temperature. Measure once an hour within 3 days after surgery and compare it with the healthy side; on days 3 to 5, Measure once every 2 hours; once every 4 hours on days 5 to 7; if the situation is normal, stop measurement after 7 days. ② Observe the skin color and capillary reaction. The reddish or bright red color of the transplanted skin indicates good blood supply; the purple-red color indicates poor venous return; the gray or pale color indicates insufficient arterial blood supply, vasospasm or obstruction. ③Observe whether there is arterial pulsation in the transplanted skin flap.