Abstract: To investigate the effects of superabsorbent polymer (SAP) on mechanical properties of engineered geopolymer composites (EGC), cube compressive test and uniaxial tensile tests were conducted on EGCs with different SAP dosages. The effects of SAP dosage on EGC compressive strength, tensile strength,and tensile stress-strain relationships were analyzed. At the same time, SEM and NMR were used to reveal the mechanism by which SAP affects the macroscopic mechanical properties of EGC.aThe results show that as the SAP content increases, the compressive strength,initial cracking strength, and ultimate tensile strength of EGC gradually decrease. At 28 days, the compressive strength, initial cracking strength, and ultimate tensile strength of EGC with the SAP content of 0.1%~0.4% is 7.4%~41.6% and 5.0%~31.7% lower than those without SAP compared to EGC specimens without SAP respectively; However,its tensile deformation capacity is significantly improved; when SAP content is 0.2%, its ultimate tensile strain reaches 7.67%,which is 34.8% higher than the specimens without SAP. Microscopic results show that the addition of SAP significantly increases the porosity proportion of large pores above 100 nm, becoming the main reason for the reduction in EGC strength. SAP can be seen as artificially introduced defects causing loose porosity in the matrix, reducing matrix fracture toughness and thereby improving EGC ductility. Simultaneously, SAP weakens the fiber bonding strength also improve the ductility of EGC.By performing linear regression analysis on the EGC tensile stress-strain test curve,the relationship expressions between SAP dosage and parameters in the model were fitted,and the tensile constitutive model considering the influence of SAP dosage was established for the internal curing EGC.