Abstract: In order to explore the effect of super absorbent resin (SAP) as an internal curing agent on the hydration process and microstructure of high-performance binder mortar system with low water-binder ratio, different amounts of pre-absorbent SAP were added into the binder mortar system (cement-fly ash-slag) with a water-binder ratio of 0.25. The hydration properties of the binder mortar system were tested by isothermal calorimetry method, chemically bound water method and X-ray diffraction (XRD). The mechanical properties and microstructure of the binder mortar system were tested by strength test, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that SAP can prolong the hydration induction period, reduce the cumulative heat release and heat release rate of the binder mortar system in the early stage, but increase the total heat release. In the early reaction, SAP will reduce the hydration degree of the binder mortar system, but its water release function can promote the later hydration and improve the total hydration degree. The early strength of binder mortar decreased with the increasing of SAP content, and the later strength increased first and then decreased with the increasing of SAP content. When the SAP content exceeded 0.3%, the compressive strength loss of the specimen increased significantly. The addition of SAP did not change the type of hydration products, but increased the content of AFt and Ca(OH)₂ in the hardened binder mortar, increased the diffusion range of the outer layer of C-S-H gel, and the edge changed from dense to loose.