[Purposes] This study aims to understand the diffusion behavior and influencing factors of the regenerant in the aged asphalt. [Methods] Using the ultraviolet aged and thermal oxygen aged asphalt as the research objects, the dynamic shear rheological (DSR) test was used to study the diffusion pattern of rejuvenators in aged asphalt to obtain a relative index characterizing the degree of diffusion. Moreover, the complex modulus recovery, which is a measure of the degree of diffusion, and the influence of aged mode, diffusion temperature, and diffusion time on the degree of diffusion are analyzed. At the micro level, the regenerant-aged asphalt diffusion system was tested by atomic force microscopy (AFM), while Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) test, and the Pearson correlation analysis was performed on the macro and micro indicators. [Findings] DSR results show that there is a diffusion gradient of the regenerant in the aged asphalt. Under the same diffusion conditions, the degree of diffusion of the regenerant in the ultraviolet aged asphalt is greater than that of the thermal oxygen aged asphalt. The higher diffusion temperature and the longer the diffusion time, the more obvious the diffusion phenomenon of the regenerant is. The microscopic test results show that with the continuation of the diffusion process, the regenerant can better restore the viscoelastic performance of the aged asphalt. Consequently, the light components inside the aged asphalt can be replenished, and the performance of the asphalt is restored. The results of Pearson correlation analysis show that the macro and micro indicators have good correlation. [Conclusions] It is a feasible method to study the diffusion behavior of regenerant in aged asphalt by combining macro and micro test methods.