"稳恒态宇宙论" can be translated into English as "Steady State Theory of the Universe" or simply "Steady State Theory" (when the context clearly refers to cosmology).
This theory posits that the universe has always existed and will continue to exist in a roughly constant state, with new matter continuously being created to maintain a constant density as the universe expands. It was a prominent alternative to the Big Bang theory in the mid-20th century but has since been largely superseded by observational evidence supporting the Big Bang model.