The old asphalt mixtures are characterized by high hardness and fine aggregate, which is aligned with the characteristics of high-modulus asphalt mixtures. In view of the current problem that the utilization rate of recycled asphalt pavement (RAP) is generally low, research on high-modulus asphalt mixtures with high RAP content was carried out. Three kinds of asphalt mixtures were prepared, including RAP addition with the content of 0%, 30%, 50% and 70% respectively, the addition of the high-modulus agent (2% asphalt mixture mass), and the addition of both RAP and the high-modulus agent with low content (1% asphalt mixture mass). Comparative experimental studies were conducted on the dynamic modulus, road performance, and fatigue performance. The results show that the dynamic modulus of asphalt mixtures increases with the rising RAP content, with mixtures containing 70% RAP meeting the dynamic modulus requirement for high-modulus asphalt mixtures (10 Hz, 15°C, |E^*| > 14,000 MPa). This enhancement for the dynamic modulus is comparable to the addition of the 2% high-modulus agent. Asphalt mixtures with 50% RAP content also satisfy the dynamic modulus requirement for high-modulus asphalt mixtures when a small amount (1%) of the high-modulus agent is added. Additionally, the increase in RAP content improves the high-temperature performance of the asphalt mixtures, and significantly increases the shear strength. However, low-temperature performance and fatigue performance are adversely affected. The research results can promote the recycling of asphalt pavement materials and the development of green maintenance technology.