A new method of real-time identification of tissue’s thermal damage level based on near infrared (NIR)scattering spectroscopy was established. Firstly, 808 nm pulse lasers of 3.5, 5, 6.5 and 8 W were introduced separately into fresh in vitro porcine livers to make thermal damage. The NIR scattering spectra and temperatures were acquired respectively during heating at a distance of 10 mm from the center of the damage, and slopes of spectra between 830 and 900 nm (S830~900) were obtained by least-square estimation. Laser was switched off as S830~900 arrived at different times of original values. Secondly, tissues around the spectra sample points were taken to obtain histological analysis, and grades were given according to the tissues’ histological characteristics using 3 grades scoring system (score of 3 means full damage, score of 2 means partial damage and score of 1 means invalid damage). Finally, Correlations among S830~900’s largest rising amplitude during heating and its final steady value after cooling and thermal damage levels were analyzed-. Results showed that a full damage was received generally as S830~900 increased more than 4 times of its original value and finally stabilized at 3.5 times after cooling; an invalid damage was usually obtained as S830~900 increased 2 to 5 times and finally dropped to 1 to 1.5 times; and others could be identified as partial damage. In conclusion, based on the analysis results, relationships between spectra and thermal damage levels were established for the first time. For thermal damage identification, S830~900’s largest rising amplitude during heating combined with its final steady value after cooling has good evaluating effects which can decrease the impact on the results induced by individual differences and make a high accuracy of above 90%. Identification of tissue’s thermal damage level in real-time with a high accurate rate has been achieved, providing a new method for in vivo monitor of tissue thermal damage.