The invention relates to the technical field of optical adhesives, in particular to an OCA optical adhesive and a preparation method thereof. The OCA optical adhesive comprises a light release film, an OCA optical adhesive layer and a heavy release film sequentially fitted from top to bottom, the OCA optical adhesive layer comprises a surface layer, a middle layer and an inside layer sequentiallyfitted from top to bottom, the upper surface of the surface layer is fitted to the lower surface of the light release layer, and the lower surface of the inside layer is fitted to the upper surface ofthe heavy release layer. The OCA optical adhesive has excellent tensile strength, curing contraction rate, resistance to cold-heat impact and scraping resistance and is excellent in light transmission and high in stability; the preparation method is simple, convenient to operate and control, stable in quality, high in production efficiency, low in production cost and suitable for large-scale industrial production.