The casing damage of gas well in Changqing oilfield is serious，and there are some problems such as poor gas tightness and difficult injection during the cement sealing process. In order to improve the air tightness and strength of epoxy resin after curing for casing damage repair，the composite resin was prepared using nano-SiO₂ doped epoxy resin for repairing gas well damage. The properties of the composite system were evaluated by rheological properties before curing，mechanical strength and plugging ability after curing，and the curing mechanism of the composite system was studied by scanning electron microscope. The results showed that the nano-SiO₂/epoxy resin composite system had the characteristics of shear dilution and viscoelasticity，and the curing time of the composite system was more than 3 h at different temperatures，providing sufficient injection time. Compared with conventional resin，the compressive strength and tensile strength of the cured nano-SiO₂/epoxy resin could reach 106.8 MPa and 72.1 MPa，and the plugging strength of pore could reach up to 37.7 MPa，which could effectively prevent formation fluid from entering the wellbore. Nano-SiO₂ could repair the micro-cracks of the cured resin，and thus improve the mechanical strength. Changqing oilfield gas well construction showed that the composite system had strong sealing and bearing capacity，which provided support for casing damaged well repair and re-fracturing wellbore reconstruction.