The invention relates to an elastic waterproof binder additive and a preparation method thereof. The product is an elastic waterproof binder additive with improved performances and prepared by stirring and mixing three components, and the preparation method comprises the following steps of: respectively stirring, mixing, filtering and packaging. The elastic waterproof binder additive disclosed by the invention has the advantages that the additive is soft inside despite its hard shell, stable in hue, moderate in consistency, good in acid resistance and alkaline resistance, and easy to control, and the like; while the elastic waterproof binder additive is used for preparing an elastic cement-base waterproof binder, the elastic waterproof binder additive also has the characteristics that after the elastic waterproof binder additive is mixed with cement powder, the obtained product is stable in hue, the binding strength of the obtained product exceeds the requirements of national standards, and the obtained product is good in acid resistance and alkaline resistance, not bloated, not thickened, long in applicable time, good in construction operating degree, not flowing, strong in flow resistance, stable in product quality, low in cost, and the like; and the elastic waterproof binder additive is applied to the ceramic tile binding of exterior wall marbles, thin porcelain plates and ceramic tiles under high-strength freezing-thawing-resisting alternated bad temperature conditions.