Poor zonal isolation due to microcracks in cement sheath is a common problem that affects oil and gas exploration and also impacts the environment. In this study, pH-sensitive superabsorbent polymers (SAPs) have been successfully synthesized through copolymerization of 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and acryloyloxyethyltrimethyl ammonium chloride (DAC) to achieve self-healing of microcracks in cement sheath. The chemical structure of p(DMAEMA-co-DAC) SAP was characterized using Fourier transform infrared (FTIR) spectroscopy. Water absorption tests determined the effect of cross-linker dosage and DMAEMA/DAC molar ratio on their water absorption rate (WAR). pH-sensitive tests showed they absorbed considerable water in neutral and weak alkaline solutions but little water in strong alkaline solutions. In addition, the WARs were quite small in high concentration calcium chloride solutions. The WARs in distilled water reduced after they were processed in cement slurry filtrate (CSF) due to hydrolysis of ester groups and the crosslinking effect of Ca2+ ions. Additionally, the SAP showed good compatibility with the cement slurry. It had little impact on the thickening time, rheological property, fluid loss, and early compressive strength of cement slurry/stone. Eventually, sealing pressure test results indicated the self-healing properties of p(DMAEMA-co-DAC) SAP-modified oil well cement. Using a 2 wt.% SAP addition, microcracks up to 166 μm can be sealed.