Nanoengineering has always been an effective way to optimize thermoelectric materials. Multi-layered nanostructures can maximize the phonon scattering efficiency and greatly reduce the thermal conductivity, thus improving the thermoelectric performance. In this work, multi-layered nanostructures are constructed in AgCuTe by alloying Cu2Se, which strongly scatters full-wavelength phonons and achieves a new low thermal conductivity at 723 K. High-resolution transmission electron microscopy shows that additional phase boundaries, multiple Moir�� fringes and regular nanophases are formed after alloying Cu2Se. Moir�� fringes form high density dislocations and strong stress fields in AgCuTe, which can greatly scatter multi-wavelength phonons. In addition, the Cu+ ions generated after the dissolution of a small amount of Cu2Se participate in the electrical transport, which optimizes the electrical performance. In the end, the AgCuTe-1%Cu2Se sample achieves the lowest thermal conductivity of ���0.45 W m���1 K���1 at 723 K, which is much lower than the average level of published AgCuTe-based materials. At the same time, between 523 K and 723 K, the average ZT ��� 1.13 of AgCuTe-1%Cu2Se reached the leading level. This work provides a new strategy for further reducing the thermal conductivity of AgCuTe-based materials.