Strain-hardening cementitious composites (SHCCs) are a class of fiber-reinforced cement-based materials with high ductility and multiple fine cracks in tension. The application of SHCCs to concrete structures is increasing for achieving better structural and durability performance. In recent years, studies also attempted to improve the self-healing effect of SHCCs by adding superabsorbent polymers (SAPs) in mixture, but the influence of SAPs on tensile behavior of SHCCs is still not fully understood. In this study, two types of SAPs, named SAP1 and SAP2, were added in the mixture of SHCCs, respectively. Compressive strength test and uniaxial tensile test were carried out for the SAP-added SHCCs. The results indicated that the SAP1 offered better strength and ductility than the SAP2 and SAP-free cases. Then, based on a micromechanics-based stochastic model proposed by past studies, uniaxial tensile behavior of SAP-added SHCCs was simulated to compare with test results on the multiple cracking process and strain hardening. By changing the micromechanical parameters related to matrix and fiber interface, the mechanism of SAPs influencing tensile properties was discussed. It is postulated that SAPs absorbed water from mortar during mixing and gradually released water to surrounding space after mortar hardening, thereby contributing to the densification of microstructure through the so-called internal curing effect. When water absorption by SAPs was sufficient, this effect also facilitated the bond between cement paste and fibers, resulting in higher ductility than the SAP-free SHCCs.