Abstract: Due to the fact that a set cement is characterized by high brittleness and large volume shrinkage after cementing, and also that the cement sheath is easily damaged during large-scale fracturing and production process, resulting in poor bonding quality and causing sustained casing pressure (SCP), etc., research on the composite material, i.e. thermosetting resin-magnesia cement was conducted. The thermosetting resin, magnesia cement skeleton material and curing agent were optimized, and a team developed coagulator and composite material of thermosetting resin and magnesia cement. An indoor test showed that the composite material had the density of 1.1–1.8 g/cm³, compressive strength of more than 14.0 MPa after 24 hours, and elastic modulus of 2–4 GPa, which can withstand stress fatigue damage of 70 MPa, and present better sealing and damage resistance than oil well cement. The field test results indicated that the composite material of thermosetting resin-magnesia cement was convenient for mixing at well site. Further, is was fully compatible with conventional well cementing equipment and process. It has with good field applicability and sealing effect. The research suggested that the composite material could completely solve the problems of oil well cement, even substitute the well cement for sealing the oil and gas layer, combined with SCP wells treatment and oil and gas wells abandonment, etc., so as to ensure the sealing integrity of oil and gas wells.