Saline–alkali soil is common in north China, especially in the Datong district in north Shanxi province. Improving the soil will benefit the environment and society. Graphene oxide (GO) has been shown to benefit agricultural and forest soils. Herein, we explore three different experimental conditions of CK (CK means irrigated with tap water), CJ (CJ means 0.2 g of bacteria addition and irrigated with tap water), and CJ25 (CJ25 means 0.2 g of composited bacteria plus 25.0 mg/L of GO added and irrigated with tap water) for saline–alkali soil by the addition of optimized amounts of GO and external bacteria. Our results show that the addition of 25.0 mg/L GO and microbial agents increases the number of bacteria and fungi in the soil and improves the species abundance of bacteria and fungi in the saline–alkali soil, while having little effect on species richness. The GO and bacterial treatment increased the abundance of Proteobacteria, Actinobacteriota, Chloroflexi, Pseudomonas, Ascomycota, Mortierella, and Fusarium. These bacteria have been shown to produce proteolytic enzymes and cellulases that decompose lignin and cellulose in litter, and thus play important roles in carbon and nutrient cycling. The addition of GO and microorganisms provides a viable way to improve saline–alkali soils.