The charge density wave (CDW), a translational symmetry breaking electronic liquid, plays a pivotal role in correlated quantum materials, such as high-$T_c$ superconductors and topological semimetals. Recently, CDWs that possibly intertwine with superconductivity and magnetism are observed in various kagome metals. However, the nature of CDWs and the role of the Fermi-surface (FS) topology in these materials remain an unresolved challenge. In this paper, we reveal the formation of CDWs in the newly discovered kagome metal ${\mathrm{LuNb}}_6{\mathrm{Sn}}_6$. We observe a ‘‘yield sign’’-like hollow triangular diffuse scattering pattern and nearly complete softening of a flat optical phonon band near ${\mathbf{Q}}_H=(1/3,1/3,1/2)$. The scattering intensity of the diffuse scattering displays divergent behavior as decreasing temperature until $T_{\text{CDW}}=70$ K, where a competing CDW at $Q_{\text{CDW}}=(1/3,1/3,1/3)$ emerges. Combined with scanning tunneling microscopy/spectroscopy and first-principles calculations, our observations support a Fermi-surface driven frustration that suppresses the leading CDW instability at ${\mathbf{Q}}_H$. This frustration is relieved by the emergence of a subleading CDW at $Q_{\text{CDW}}$. These results provide insights into the interplay between the Fermi surface, strong electron-phonon coupling, and charge density wave formation in quantum materials.

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• Charge density waves
• Fermi surface
• Kagome metal
• Angle-resolved photoemission spectroscopy
• First-principles calculations
• Scanning tunneling microscopy
• X-ray techniques