Ｒejuvenator adjusts the components of the aged asphalt through diffusion and miscibility，so as to restore its road performance and make it meet the application requirements． Therefore，the diffusion of rejuvenator is the main technical problem influencing the regeneration effect of aging asphalt． Firstly，an analysis method of rejuvenator diffusion coefficient was established by using Fourier transform infrared spectroscopy technique and taking the characteristic absorption peak area as the measurement standard． Then，using CTBN as a tracer，a self-designed diffusion test was used to quantitatively analyze the diffusion amount of the rejuvenator with the characteristic absorption peak intensity，and calculate the rejuvenator diffusion coefficient． The results show that the characteristic peak at 1739cm － 1 of the infrared spectrum of the rejuvenator change significantly after CTBN labeling，and the peak area shows a linear relationship with the change of CTBN content． The diffusion amount of rejuvenator in aged asphalt can be effectively reflected by establishing a standard curve． Taking the peak area ratio D1739 /D1458 as the measurement standard，the established theoretical analysis method of the rejuvenator diffusion coefficient has certain reliability． The diffusion coefficient is closely related to the concentration change，and can effectively reflect the degree of aging asphalt regeneration． The diffusion coefficient and the cumulative diffusion amount are proportional to the temperature change，and the growth rate of the two is basically the same． The diffusion rate at the same temperature shows a decreasing trend with the increase of the vertical depth． It is consistent with the change trend of the rejuvenator diffusion amount，and is in compliance with Fick’s second law．