A novel acidic-stable covalent organic framework (COF-205-Ru) was developed to stabilize atomic Ru species for efficient acidic water oxidation. The COF-205-Ru was constructed by incorporating atomically dispersed Ru species into a 2D COF with unique crossed π-conjugation. This structure suppresses Ru dissolution through strong Ru-N bonds and reduces Ru oxidation state via π-conjugation, stabilizing oxygen vacancies during oxygen evolution. Experimental and theoretical analyses revealed that COF-205-Ru exhibits enhanced oxygen activation, reduced oxygen vacancy formation energy, and improved electrochemical stability. The catalyst demonstrated a high mass activity of 2659.3 A g⁻¹, 32 times higher than commercial RuO₂, and long-term durability over 280 hours. The unique crossed π-conjugation in COF-205-Ru enhances electron delocalization, stabilizes oxygen vacancies, and lowers the energy barrier of the rate-determining step for acidic water oxidation. This work provides a strategy to simultaneously enhance the stability and activity of Ru-based catalysts for acidic water oxidation. The study highlights the importance of structural design in achieving efficient and durable electrocatalysts for water splitting applications.A novel acidic-stable covalent organic framework (COF-205-Ru) was developed to stabilize atomic Ru species for efficient acidic water oxidation. The COF-205-Ru was constructed by incorporating atomically dispersed Ru species into a 2D COF with unique crossed π-conjugation. This structure suppresses Ru dissolution through strong Ru-N bonds and reduces Ru oxidation state via π-conjugation, stabilizing oxygen vacancies during oxygen evolution. Experimental and theoretical analyses revealed that COF-205-Ru exhibits enhanced oxygen activation, reduced oxygen vacancy formation energy, and improved electrochemical stability. The catalyst demonstrated a high mass activity of 2659.3 A g⁻¹, 32 times higher than commercial RuO₂, and long-term durability over 280 hours. The unique crossed π-conjugation in COF-205-Ru enhances electron delocalization, stabilizes oxygen vacancies, and lowers the energy barrier of the rate-determining step for acidic water oxidation. This work provides a strategy to simultaneously enhance the stability and activity of Ru-based catalysts for acidic water oxidation. The study highlights the importance of structural design in achieving efficient and durable electrocatalysts for water splitting applications.