Altermagnetism, the third class of collinear magnetic order, uniquely combines a zero net magnetization with spin-polarized bands in reciprocal space, opening new avenues for two-dimensional valleytronics and spintronics. Here, using first-principles calculations, we predict that the Janus monolayer ${\mathrm{Cr}}_2\mathrm{SSe}$, which possesses intrinsic inversion symmetry breaking, hosts a strain-tunable multipiezo effect and exhibits distinctive valleytronic properties. The system displays pronounced spin splitting and band inversion at the $X$ and $Y$ high-symmetry points in the Brillouin zone, giving rise to robust spin-valley locking. The degeneracy of these valleys is protected by diagonal mirror symmetry. The application of uniaxial strain breaks this symmetry, concurrently inducing piezovalley, piezoelectric, and piezomagnetic responses, a manifestation of the multipiezo effect. Critically, strain applied along orthogonal crystallographic directions yields opposite valley polarization, while under small compressive strain, we achieve selective reversal of valley polarization, enabling independent control of valence and conduction band valleys and promoting a single-spin-channel anomalous valley Hall effect. These findings establish a pathway for low-power, nonvolatile manipulation of valley degrees of freedom and enhanced spin transport efficiency, providing a theoretical foundation for the design of energy-efficient valleytronic devices.

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• Altermagnetism
• Anomalous Hall effect
• Magnetism
• Valley degrees of freedom
• First-principles calculations