To find traffic conflict identification indicator which can reflect driver's mental load and traffic conflict identification method based on the indicator, the correlation between the conflict stimuli and the pupil diameter is identified by comparative analysis, a pupil diameter based GSA-T fast traffic conflict identification method is proposed to remedy the defects of original GSA to meet the requests of traffic conflict identification. The result of construction conflict shows that the computation and the identification time of the GSA-T is shorter than the Enumeration method, thus the low time complexity and space complexity are testified. It is proved that GSA-T can meet the requests of traffic conflict identification and road safety evaluation, and can lay foundation for further study of relationship between traffic conflict severity and pupil diameter.