The invention relates to the field of material surface modification, and discloses alkenyl silicon phosphine oxide and a preparation method thereof, and alkenyl silicon phosphorus-vinyl acetate copolymer emulsion and a preparation method and application thereof. The alkenyl silicon phosphine oxide is prepared from hydroxyl phosphine oxide and an alkenyl silane coupling agent; the alkenyl silicon phosphine oxide and vinyl acetate are copolymerized to obtain the alkenyl silicon phosphorus-vinyl acetate copolymer emulsion, the copolymer emulsion contains rich silicon and phosphorus elements, thesilicon and phosphorus are synergistically flame-retardant, and the obtained copolymer emulsion can be used as a material surface modifier and has excellent thermal stability, hydrolysis resistance and hydrophobicity. The copolymer emulsion is applied to the surfaces of materials such as paper, fabrics, wood and the like, and can endow the materials with excellent surface properties and flame retardancy. The preparation method of the copolymer emulsion provided by the invention is simple in process, low in cost, green and environment-friendly, wide in application range and easy for industriallarge-scale popularization, and has a good application prospect and great market competitiveness.