The invention discloses a Chinese angelica polysaccharide derivative and a synthesis method therefor. The derivative is represented by a formula I shown in the description, wherein n is an integer from 80 to 130. The invention further discloses an application of the derivative. The synthesis method for the derivative is simple and effective and is easy in operation; the derivative is good in chemical stability, good in water solubility, high in specific activity and high in biological activity; and by applying the Chinese angelica polysaccharide derivative to in-vivo SPECT imaging and SPECT/CT, the in-vivo distribution of Chinese angelica polysaccharides can be clearly observed, and the Chinese angelica polysaccharides are mainly concentrated in a liver, so that the condition that the Chinese angelica polysaccharides can serve as a liver-targeted drug carrier is confirmed, and the research on natural macromolecular polysaccharide nuclein markers is promoted.