Phosphogypsum-based excess-sulphate slag cement (PESSC), as a non-calcined cementitious material, offers benefits such as minimal heat release, great volumetric stability, and significant resistance to sulphate erosion. Nonetheless, its application is constrained by prolonged setting periods, inadequate carbonation resistance, and poor stability of long-term performance due to the persistent release of impurity derived from phosphogypsum, as well as the sulphate-rich and low alkalinity hydration environment. Recently, effective strategies are needed to regulate the hydration environment of PESSC, enhance the formation of highly stable hydrates, optimise the microstructure of matrix, and provide systematic design theories and performance regulation methodologies. This study focuses on the impact of impurity release on gypsum crystallisation and the hydration hardening of PESSC, as well as the mechanisms and performance advancements of alkali and sulphate-activated slag, bases on the fundamental physical and chemical features of the raw components. A comprehensive discussion is presented on the feasibility of accelerating condensation through phosphogypsum pretreatment, promoting sustainable reactions by adding appropriate alkali-activators to regulate the hydration environment, enhancing the long-term performance and durability of PESSC by synergizing multiple components, and generating stable hydrates by incorporating modifiers. This work seeks to offer theoretical and technological support for the development of new theories and methodologies for PESSC design and large-scale applications.