Super absorbent polymer （SAP） was used as the internal curing material for concrete. Through the nanoindentation test， the effects of curing age and SAP content on the micromechanics of the cavity interface of the internally cured concrete were studied， and the internal phase and chemical composition of the concrete were characterized by scanning electron microscope and energy dispersive spectroscopy （SEM-EDS）. The results show that the elastic modulus and hardness of the SAP water release interface increase with the increase of curing age. After adding SAP， the distribution of hydration products in concrete becomes more uniform. As the curing age increases， the content of hydration products gradually increases， and the interface becomes denser. The SEM-EDS test results are consistent with the test of mechanical properties， indicating that SAP has a positive impact on high-strength concrete.