As a non-invasive technique for the measurement of blood and oxygen in tissue, the near-infrared spectroscopy (NIRS) has an increasing application to the postoperative monitoring of plastic surgery. In authorial research, a set of NIRS oximeter has been used in 6 successful flap-transplantation operations to monitor and contrast the oxygen saturation in the free flap side and in the normal opposite side. It was found in the research that there is a notable difference in the oxygen saturation between those two sides. Another research has been done in an unsuccessful operation. In this experiment, several points in the mandible were measured and the result shows that the oxygen saturation is at an obviously lower level in the anoxic position than in the normal ones. In the above several researches, near infrared spectroscopy showed a high sensitivity to detect the dynamic changes in flaps induced by inhalation of pure oxygen. Therefore, NIRS can be a valuable aid in the post-operative monitoring of free flap after the operation, and must have a great practical future in this field.