The invention discloses a waterproof sealant at joints of prefabricated external wall panels of prefabricated buildings and a production process of the waterproof sealant. The waterproof sealant comprises an MS polymer, polyether polyol, nano calcium carbonate, polyamide wax, a coupling agent, a catalyst, fumed silica, dibutyltin dilaurate, nano diatomite, an antibacterial agent, a cross-linking agent, a flame retardant, an ultraviolet absorbent, a curing agent, a curing accelerator and absolute ethyl alcohol. The waterproof sealant at the joints of the prefabricated external wall panels of the prefabricated buildings has the advantages of high waterproof performance, good weather resistance, high cohesiveness, short surface drying time, high tensile strength, high elongation at break, high hardness, high corrosion resistance, high falling resistance, long service life, no toxicity, low cost and the like, and is suitable for large-scale popularization and application. The sealant is ahigh-performance waterproof sealant; the sealant has the advantages that the stress is mild, the sealant has stress and elasticity at the same time, and even if the sealant is in a stretched state fora long time, the influence caused by shrinkage of building base materials can be eliminated to the maximum extent under the action of stress relaxation.