Abstract: The present invention provides an insulin-containing buccal spray and the preparation method thereof. The insulin buccal spray of the invention is a microemulsion having the average diameter of less than 200 nm, comprising 10000 u-7000 u of insulin, 5-50 g of soybean lecithin as absorption promoter, 20-80 g of propylene glycol as cosolvent, and balanced with phosphate buffer of pH 6.8-7.8 to 1000 ml, based on 1000 ml microemulsion. The preparation method comprises: a) adding soybean lecithin to propylene glycol, mixing sufficiently, then adding phosphate buffer to result solution, and sonicating, thus obtaining the oil phase of the microemulsion; b) dissolving insulin in phosphate buffer, c) adding the insulin solution to the oil phase, sonicating again, thus obtaining the emulsion of the invention. The efficiency and stability of the emulsion of the invention are improved significantly, and administration of the invention is convenient.