A construction method for reinforcing a loess embankment by combining microbial mineralization with phosphogypsum. The method includes: (1) placing Bacillus pasteurii in a culture medium to prepare a microbial solution, and mixing urea, calcium chloride and water to prepare a cementing solution; (2) mixing a mixture, the microbial solution and water well, and adding the cementing solution and water to prepare an improving mixture; and (3) leveling and compacting an original ground; laying a geomembrane, the improving mixture and a geogrid; laying a last geomembrane on the top of the embankment after the embankment is laid, and then laying a roadbed. The method meets the improvement and construction requirements of loess embankments of high-grade highways, and reduces the stock of phosphogypsum, thereby reducing the occupation of cultivated land. The microbial improvement of the phosphogypsum achieves the immobilization of harmful elements, thereby reducing environmental pollution.