The invention relates to a method for preparing cobamamide. The method comprises the following steps of: a, taking vitamin B 12 fermentation solution, and hydrolyzing and filtering under the light-resistant condition; b, adsorbing filter liquor by using a macroporous resin column, and washing and desorbing to obtain primary desorption solution; c, evaporating and concentrating the primary desorption solution to obtain concentrated solution; d, adding a flocculating agent into the concentrated solution for filtering to obtain purification solution; e, adsorbing the purification solution by using a chromatographic resin column, and developing and desorbing to obtain secondary desorption solution; f, adsorbing the secondary desorption solution by using an aluminum oxide column, and developing and desorbing to obtain crystallizing stock solution; and g, adding acetone into the crystallizing stock solution with stirring for crystallizing, and filtering and drying to obtain a finished product. The impurity content of a product obtained by the method is below 1.0 percent, the cobamamide content is over 98.0 percent, the yield of the product is over 50 percent, and the total yield of vitamin B 12 is over 80 percent. The method has the characteristics of simplicity, convenience, easy operation, high extraction yield, high purity of the product and low production cost.