Coupler, also known as "color coupler"，is an organic dye intermediate ，which can form a color screen as a kind of color photographic material. After the exposing of the photosensitive material, the color developer reacts with the silver halide to form their oxidation product. And then the oxidation product reacts with the color developing agent, couplers, to obtain the corresponding color images. Generally, there are yellow, magenta, cyan three basic couplers. Couplers can be classified into many kinds according to the dye colors, can be divided into antithesis and even outside types according to the method of use, and can be divided into several types of oil-soluble, water-soluble and polymers. Now the early used water-soluble coupler has gradually been replaced by the oil-soluble coupler, which is more vivid and saturated. And they are mainly used for the production of color filmstrip and color film.