The invention discloses an oil-in-water type nanometer emulsion adjuvant and MRSA nanometer emulsion adjuvant vaccine and a preparing method thereof. The nanometer emulsion adjuvant is prepared from, by mass, 1-30% of surface active agent, 0.1-15% of cosurfactant, 0.1-15% of oil phase and 40-98.8% of water; the adjuvant is clear and transparent liquid from appearance, the particle size ranges from 1 nm to 100 nm, viscosity is low, the adjuvant belongs to a highly thermodynamics stabilizing system, and therefore high-speed centrifugation is stable without layering; when being compatible with the vaccine, the adjuvant can wrap the vaccine or be directly mixed with the vaccine physically for use, and immunity can be achieved by means of administration routes such as intramuscular injection and nasal drip. The adjuvant has the advantages of being low in cost, convenient to administrate, small in toxicity, good in liquidity and small in irritation to organism, and avoiding cross infection, the immune effect and stability of the vaccine are effectively improved, and the adjuvant has a wide application prospect.