The invention discloses latex for waterborne exterior-wall primer and a preparation method and application thereof. The latex comprises, by weight, 20-50% of resin, 20-40% of activated diluents, 5-10% of photoinitiators, 5-10% of filler, 10-20% of mixed solvents and 2-5% of auxiliaries. The latex for the waterborne exterior-wall primer prepared according to the above formula is good in closure performance, high in adhesive force and infiltration capacity, highly resistant to alkali burnout and water, good in watertightness, outstanding in salting-out resistant effect, remarkable in interlayer collocation effect and capable of effectively avoiding the defects of poor lasting effect, instable interlayer collocation, failure in reaching the standard of VOC (volatile organic compounds) and the like when common latex is used for the primer, thereby being a good binder for preparing excellent waterborne primer.