The invention discloses modified acrylic resin for a weather-resistant coating and a preparation method for the same. Fluorine atoms and silicon atoms are introduced in acrylic resin simultaneously, thus improving the comprehensive performances of water resistance, pollution resistance, solvent resistance, weather resistance and the like, making up the defects of silicon resin, fluorine resin and acrylic resin used as coatings independently, and completely enabling the modified resin to be used as a protective coating applied to reinforced concrete and building external walls in the conditions of the atrocious weathers of exposure, cold wave, acid, alkali, salt and the like. The preparation method disclosed by the invention is simple in process, low in equipment requirement and abundant and easily available in raw materials, and has no need of pre-emulsification or a high-speed shearing machine; and because silicon resin is synthesised at first, the gels caused by the hydrolysis of a silane coupling agent can be effectively suppressed, the reaction conversion rate is high, the amount of the gels is low, the emulsion stability is good, and the reaction process is easy to control. The preparation method is especially suitable for industrialized production.