The invention discloses a preparation method of a slow release nutritional agent for increasing the biochemical treatment effect of chemical industry production wastewater. The preparation method comprises the following steps of adding deionized water in reaction equipment, heating to 45 to 55 DEG C, adding the following ingredients in percentage by weight in sequence: 5 to 10 percent of glucose, 0.5 to 5 percent of sodium acetate, 0.5 to 5 percent of sodium citrate, 0.5 to 5 percent of calcium lactate, 0 to 5 percent of NH4Cl, 0 to 5 percent of K2HPO4 3H2O, 1 to 5 percent of MgSO4, 0.5 to 5 percent of FeSO4, 5 to 10 percent of Na2CO3, 0.1 to 1 percent of CuSO4, 0.1 to 1 percent of ZnSO4, 0.5 to 1 percent of MnSO4 H2O, 0.1 to 0.5 percent of CoSO4 7H2O, 0.1 to 0.5 percent of (NH4)6Mo7O24 4H2O, 0.01 to 0.05 percent of vitamin C and 0.01 to 0.05 percent of vitamin VH, and stirring rapidly and uniformly; then stirring at a low speed, adding roasted expanded graphite, forming granules of which the grain diameter is 0.7 to 2.0 mm through a pelletizer, spraying and coating the granules by adopting a mixed solution of polysaccharide derivatives and polyacrylamide, mixing the granules with the raw materials for secondary pelletizing and enveloping after drying, thus obtaining granules of which the diameter is 2.0 to 4.0 mm. A biological nutritional agent prepared by the invention is convenient and safe in preservation and use, degradation is thoroughly utilized, the microbial activity and the treatment effect of a biochemical unit can be remarkably increased, and the effective utilization rate is high.