Machined surface integrity， a composite reflection of the geometric， physical， chemical， and mechanical properties of the machined surface layers， is dictated by the thermo-mechanics loads and material removal modes inherent to the cutting processes. This integrity directly governed the in-service performance and lifespan of engineered components. A thorough investigation into how conditioning strategies influenced surface integrity was therefore fundamental to realize high-integrity surfaces， and was critically important for optimizing the machining of difficult-to-cut metallic materials. This review began by categorizing the metrics of machined surface integrity for these materials based on three aspects： geometric features， microstructural evolution， and surface-layer mechanical properties， while also summarizing the approaches for developing predictive models. Subsequently， it elucidated research advancements in machined surface integrity conditioning strategies of difficult-to-cut metallic materials， critically comparing the distinct influence mechanisms of tool and process optimization， multi-energy field assisted machining， and workpiece pre-treatment on machined surface integrity. Finally， this paper explored the prediction accuracy of current models and the general applicability of conditioning strategies， offering an outlook on future research priorities.
