The invention discloses a novel plant nitrogen-fixing bacterium fertilizer and a preparation method thereof. The novel plant nitrogen-fixing bacterium fertilizer is prepared from expanded vermiculite,distillers' grains,animal waste,straw,pond bottom mud,molasses,wheat bran,bean pulp,microorganism complex microbial inoculants,large-pore resin and micro elements. The microorganism complex microbialinoculants include bacillus mucilaginosus,azotobacter chroococcum,bacillus laterosporus,bacillus amyloliquefaciens,yeasts and lactobacillus plantarum. Compared with the prior art,the formula of the plant nitrogen-fixing bacterium fertilizer is reasonable,the plant nitrogen-fixing bacterium fertilizer has the effects of dissolving phosphorus,releasing potassium and fixing nitrogen,and absorption and convention of nitrogen,phosphorus and potassium of plants are remarkably promoted; by improving the soil structure,breathability and water retention of soil are improved,the plant disease and insectpest occurrence rate is decreased,and plant growth and development are promoted. Experiments show that the adopted nitrogen-fixing bacterium fertilizer can remarkably increase the crop yield,lower the plant disease and insect pest occurrence rate,and shorten the growth period.