The invention discloses a compound microorganism fungicide for improving the water quality of a culturing water body and a preparation method. The compound microorganism fungicide is prepared by taking the strains by weight percent: bacillus subtilis, yeast, lactic acid bacteria, photosynthetic bacteria, nitrifying bacteria, bacillus licheniformis, and the like. The preparation method comprises the following steps of: firstly, culturing the bacillus subtilis and bacillus licheniformis: culturing the bacillus subtilis and bacillus licheniformis on a beef extract peptone culture medium; secondly, culturing the yeast: culturing the yeast on a lactic acid-potato-glucose culture medium; thirdly, culturing the lactic acid bacteria: culturing the lactic acid bacteria on a wort culture medium, inoculating on a triangular flask for culturing, and finally inoculating on a solid culture medium for culturing; fourthly, culturing the photosynthetic bacteria; fifthly, culturing the nitrifying bacteria; and sixthly, stirring and mixing the cultured strains by weight ratio, and drying at low temperature, thereby obtaining the compound microorganism fungicide. The formula is reasonable; the use is convenient; water is uniformly splashed; the method is easily performed; and the operation is convenient.