As　the　anode　reaction　of　proton　exchange　membrane　water　electrolysis　(PEMWE),　the　acidic　oxygen　evolution　reaction　(OER)　is　one　of　the　main　obstacles　to　the　practical　application　of　PEMWE　due　to　its　sluggish　four-electron　transfer　process.　The　development　of　high-performance　acidic　OER　electrocatalysts　has　become　the　key　to　improving　the　reaction　kinetics.　To　date,　although　various　excellent　acidic　OER　electrocatalysts　have　been　widely　researched,　Ir-based　nanomaterials　are　still　state-of-the-art　electrocatalysts.　Hence,　a　comprehensive　and　in-depth　understanding　of　the　reaction　mechanism　of　Ir-based　electrocatalysts　is　crucial　for　the　precise　optimization　of　catalytic　performance.　In　this　review,　the　origin　and　nature　of　the　conventional　adsorbate　evolution　mechanism　(AEM)　and　the　derived　volcanic　relationship　on　Ir-based　electrocatalysts　for　acidic　OER　processes　are　summarized　and　some　optimization　strategies　for　Ir-based　electrocatalysts　based　on　the　AEM　are　introduced.　To　further　investigate　the　development　strategy　of　high-performance　Ir-based　electrocatalysts,　several　unconventional　OER　mechanisms　including　dual-site　mechanism　and　lattice　oxygen　mediated　mechanism,　and　their　applications　are　introduced　in　detail.　Thereafter,　the　active　species　on　Ir-based　electrocatalysts　at　acidic　OER　are　summarized　and　classified　into　surface　Ir　species　and　O　species.　Finally,　the　future　development　direction　and　prospect　of　Ir-based　electrocatalysts　for　acidic　OER　are　put　forward.　Conventional　and　unconventional　acidic　OER　mechanisms　such　as　AEM,　dual-site　mechanism,　and　LOM　are　fully　analyzed,　and　relevant　Ir-based　electrocatalyst　optimization　strategies　are　summarized　and　classified　from　the　perspective　of　these　reaction　mechanisms.　Further,　the　active　species　of　Ir-based　electrocatalysts　in　acidic　OER　are　discussed　and　summarized.　Finally,　the　future　research　direction　and　prospect　of　Ir-based　electrocatalysts　are　presented.　image