The invention relates to the technical field of preparation of high-toughness low-temperature fast-curing epoxy adhesives for bonding inert materials, and discloses a preparation method of a high-toughness low-temperature fast-curing epoxy adhesive for bonding inert materials. The epoxy resin component comprises 80%-94.5% of epoxy resin containing long-chain alkyl and polyurethane, 5%-19.5% of low-viscosity flexible epoxy resin and 0.5%-1% of a coupling agent a, and the low-viscosity flexible epoxy resin enhances the flexibility, crack resistance and mechanical properties of the material; the curing agent component comprises 80%-90% of polythiol, 1%-5% of monohydramine, 5%-15% of tertiary amine urea, 0.5%-1% of a coupling agent b and 0.1%-1% of a defoaming agent, the polythiol provides a rapid curing characteristic, the monohydramine and the tertiary amine urea synergistically enhance the toughness and chemical stability of a curing network, the coupling agent b improves the adhesion, and the defoaming agent avoids bubbles. By combining the weakly acidic coupling agent and the strongly acidic coupling agent, different monohydramine and tertiary amine urea are selectively used, and the curing rate, the mechanical strength and the flexibility are optimized.