［Purposes ］ Given the widespread water damage in early pavement distress and its significant restriction on pavement lifespan and service performance，this paper aims to provide a basis for optimizing the design and application of recycled mixtures by analyzing the effect of the blending degree of new and aged asphalt on the water stability of recycled hot -mix asphalt mixture （RHAM）.［Methods］ First，the blending degree of new and aged asphalt during the hot -mixing process was quantitatively analyzed using a Fourier transform infrared spectrometer （FTIR）.Then，the FTIR results were validated using a dynamic shear rheometer （DSR）.Finally，the porosity，indirect tensile strength （ITS），and tensile strength ratio （TSR） of the mixtures with different blending degrees were evaluated through freeze -thaw cycle tests.On this basis，the relationship between the blending degree of new and aged asphalt and the water stability of RHAM was established.［Results］ Extending the mixing duration and reducing the content of reclaimed asphalt pavement （RAP） can effectively improve the blending degree of new and aged asphalt，thereby enhancing the water stability of the mixture.When the blending degree is greater than 81.6%，the increment in porosity of RHAM decreases with the increase in the number of freeze -thaw cycles.However，under the condition of a low blending degree，the freeze -thaw action leads to a significant increase in porosity and a significant decrease in TSR and water stability.［Conclusions ］ The blending degree of new and aged asphalt is a key factor affecting the water stability of RHAM.A higher blending degree can significantly improve the resistance of the mixture to water damage.This paper provides a theoretical basis for the mix design and process control of recycled asphalt mixture，which helps to extend the pavement service life and improve its service performance.