The combination of sliding ferroelectricity and valley properties holds significant potential for the development of next-generation ultrafast processors and memory devices. However, the traditional ferroelectric polarization based on special symmetry can reduce valley polarization. In this study, we propose the across-layer sliding ferroelectricity and robust valley polarization in inversion-symmetric lattices through symmetry analysis and first-principles calculations. In the case of trilayer or more layers, across-layer sliding can induce asymmetry, thereby breaking the overall $P$ symmetry, and ferroelectric polarization occurs. Intriguingly, for the antiferromagnetic even layers, the valley polarization is insensitive to $PT$ symmetry, allowing the coexistence of across-layer sliding ferroelectricity and robust valley polarization. We confirm this in real multilayer ${\mathrm{YI}}_2$ configuration through first-principles calculations. This finding provides a platform for the research sliding ferroelectricity and valleytronics.

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• Electric polarization
• Ferroelectricity
• First-principles calculations
• Valley degrees of freedom
• 2-dimensional systems
• Density functional theory