NOVELTY - A biological compound fertilizer is prepared by mixing prepared phosphogypsum with pre-processed livestock and poultry feces or pre-processed crop stalks or the pre-processed livestock and poultry feces and crop stalks to obtain mixture; stirring the mixture, and adding water; piling the prepared mixture for fermentation, fermenting for 14-20 days in summer and 25-35 days in spring or autumn, and obtaining fermented mixture; sterilizing culture medium and collecting mixed microbes; and mixing mixed microbes with the fermented mixture.    USE - Biological compound fertilizer containing phosphogypsum used in field crops for improving structures of saline-sodic soil, acidic soil, and coastal soil (claimed).    DETAILED DESCRIPTION - Biological compound fertilizer containing phosphogypsum, is prepared by (A) adjusting pH value of phosphogypsum to 4-5 by using limewater, drying and pulverizing to 200-400 meshes, air-curing livestock and poultry feces, cutting crop stalks into pieces, and air-curing; (B) mixing the prepared phosphogypsum with pre-processed livestock and poultry feces or pre-processed crop stalks or the pre-processed livestock and poultry feces and crop stalks to obtain mixture, a ratio of phosphogypsum to livestock and poultry feces being 30-50:50-70, ratio of phosphogypsum to crop stalks being 20-50:80-50, and a ratio of phosphogypsum to livestock and poultry feces and crop stalks being 30-50:10-20:60-30; (C) stirring the mixture, and adding 35-65 wt.% of water; (D) piling the prepared mixture for fermentation, fermenting for 14-20 days in summer and 25-35 days in spring or autumn, and obtaining fermented mixture; (E) sterilizing culture medium, controlling culturing temperature at 28-32 degrees C, inoculating (i) 2.5-8 wt.% of Bacillus cereus, 2-7 wt.% of nitrobacteria, and 1.5-6.5 wt.% of Clostridium of the culture medium, and culturing for 3-4 days; (ii) inoculating 2-8 wt.% of B. megaterium and 2.2-6.8 wt.% of B. mucilaginosus of the culture medium, and culturing for 2 days; (iii) inoculating 2.5-7.5 wt.% of Pseudomonas fluorescens and 2.5-7.5 wt.% of P. aeruginosa of the culture medium, and culturing for 2-3 days; (iv) inoculating 1.5-6 wt.% of Klebsiella, 2-8 wt.% of rhodospirillaceae, 3-6 wt.% of Azotobocter chroococcum, and 1.5-7 wt.% of Cyanobacterium of the culture medium, and continuing to culture for 3-5 days; and (v) inoculating 2-9 wt.% of Trichoderma harzianum and 2-8.5 wt.% of Glomus versiforme of the culture medium, continuing to culture for 2 days, and collecting to obtain mixed microbes; and (F) mixing the mixed microbes with the fermented mixture at a weight ratio of 1: 00-1000, adding water to adjust water content to be 35-45%, uniformly stirring, piling for 3-5 days at room temperature for secondary co-fermentation, air-curing until water content is 20-30%, and pulverizing to obtain powder mixture.