In order to improve the flame retardancy of EPS insulation materials, different volume ratios of magnesium oxychloride cement (MOC) were added to EPS and its properties were studied. The results show that the mechanical properties of EPS insulation materials gradually increase with the increase of MOC volume ratio. As the volume ratio of MOC increases, the dry density and thermal conductivity of EPS insulation materials continue to increase, indicating a continuous decrease in insulation performance. The limited oxygen index (LOI) of pure EPS is only 18.1%. As the MOC volume ratio increases, the LOI of EPS insulation material gradually increases and combustion becomes more difficult, significantly improving its flame retardancy. When the MOC volume ratio is 9%, EPS insulation material can self extinguish in a short period of time. As the volume ratio of MOC increases, the combustion performance level of EPS insulation materials gradually increases from flammable B₃ level to non flammable A₂ level. Based on the requirements for the performance of EPS insulation materials in JG/T 536—2017, when the volume ratio of MOC is 9%, the comprehensive performance of EPS insulation materials is optimal. At this time, the compressive strength and tensile strength of EPS insulation materials are 0.256 MPa and 0.198 MPa, respectively, with a dry density of 149 kg/m³, a thermal conductivity of 0.055 3 W/(m·K), and a flame retardant grade of A₂.