The invention discloses a method for synthetizing dextran selenium polymers by an enzyme means. According to the method for synthetizing the dextran selenium polymers by the enzyme means, dextran sucrase is used as a catalyst; sucrose and sodium selenite are used as substrates; and then, enzymatic reaction is carried out so as to synthesize the dextran selenium polymers. By catalyzing the sucroseand the sodium selenite by using the dextran sucrase, the method is capable of synthesizing the dextran selenium polymers in one step. Tests have proven that the method for synthesizing the dextran selenium polymers by the enzyme means overcomes the problems of complex reaction steps, intense reaction conditions, relatively many byproducts and the like of chemical synthesis; moreover, the method has the characteristics of being simple in reaction system, wide in raw material source, mild in reaction conditions, relatively high in selenization efficiency, relatively high in selenium polymer yield and the like. In addition, the method is capable of reducing usage of toxic chemical agents as reaction media; moreover, relatively few byproducts are produced so as to facilitate separation and purification, so that, no environmental pollution is caused.