AbstractShield tunnels have been extensively used in many fields and are exposed to the threat of earthquakes. Seismic isolation is an effective anti-seismic method to protect tunnels from earthquake damage. This study investigates asphalt-cement (A-C) materials used as a seismic isolation layer of a shield tunnel by backfill grouting. Both a uniform test and comparative test were conducted to study the grouting properties of A-C materials. The experimental results indicated that an increase in cement content significantly affects the fluidity and consistency of A-C materials. The ultimate compressive strength increased with increasing cement content, and the recommended mass ratio of cement/asphalt for the seismic isolation layer was 50%. Then, a planned shield tunnel crossing hard-soft stratum junction was taken as the research object, and the seismic response of the tunnel lining with different fortified lengths of A-C seismic isolation layer was analyzed by numerical simulation. The calculation results show that the tunnel lining located at the hard-soft stratum junction is vulnerable to damage under seismic action, and the A-C seismic isolation layer can significantly reduce the maximum principal stress of lining near the junction. The reasonable fortified length of the A-C isolation layer for the examined shield tunnel is 3.5 times the tunnel diameter from the stratum junction to both sides.