As an important stage of a wellbore completion, the quality of oil well-cementing (cementation) is closely related to the performance of the cement sheath, as the cement sheath is responsible for providing complete zonal isolation. Well cement failure and interfacial debonding between the cement and casing and cement and rock formations can lead to a barrier failure. As an emerging low-cost, green fracturing technology, methane deflagration fracturing technology places higher demands on the cement sheath, with impact resistance surpassing that of hydraulic fracturing (HF) and permeability exceeding that of explosive fracturing (EF). This paper optimized the formulation of a cement slurry system with additives to develop elastic toughened impact-resistant and gas channeling-resistant cementing cement slurry suitable for deflagration fracturing. Laboratory experiments were carried out on basic and modified cement slurries, including uniaxial and triaxial compression tests, permeability measurements, and dynamic compression tests using a Split Hopkinson Pressure Bar (SHPB). Compared to the standard slurry, the modified toughened cement slurry showed only a slight decrease in compressive strength, a significant reduction in elastic modulus, enhanced impact resistance, and lower permeability. This cement slurry system effectively resists external loads, enhances elasticity and toughness, maintains low permeability and high-impact resistance. It meets the requirements for well cementing while preserving the integrity of the cement sheath under the impact loads of methane deflagration fracturing.