The invention belongs to the field of asphalt modifiers, and particularly relates to styrene-butadiene latex and a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: a) mixing an emulsifier, a molecular weight regulator, a dispersing agent, a free radical stabilizer, an electrolyte and water, regulating the temperature, and adding butadiene, styrene, a tertiary amine monomer and an initiator into the mixed system for reaction when the temperature of the mixed system reaches 5-15 DEG C, b) after the reaction is carried outfor 4-6 hours, adding a cross-linking agent into the reaction system, then heating to 20-40 DEG C, and continuously reacting for 0.5-2 hours, and c) after the reaction is finished, mixing the obtained reaction product with an anti-aging agent, and degassing to obtain the styrene-butadiene latex. According to the method provided by the invention, by adopting a low-high temperature two-stage methodfor polymerization, adding a proper amount of tertiary amine monomer to participate in copolymerization and adding a proper amount of organic matter containing an active halogen group as a cross-linking agent, the prepared styrene-butadiene latex has relatively high solid content and excellent asphalt modification capability.