Cross-feeding is a common relationship among microbial species, in which species use metabolites of other members in the environment to promote their own growth is called metabolic cross-feeding relationship. Metabolic cross-feeding relationship often has a great influence on the competition between species and even changes the population structure. In order to study the role of metabolic cross-feeding relationships in maintaining microbial species diversity, we constructed the resource competition models with different cross-feeding relationships. These models not only reflect the dynamics of population size and resource quantity when microbial species compete for resources, but also show the influence of species' utilization of metabolic resources from other competitors on their own living status. Then we carried out numerical simulation on the models, and the results show that:(1) we consider different cross-feeding structures in microorganisms:unidirectional cross-feeding and bidirectional cross-feeding between two species and multidirectional cross-feeding between multiple species. The simulation results indicate that different cross-feeding relationships can promote the stable coexistence of competing species. On the one hand, by using the metabolites of other competitive members, the disadvantaged species can break the restriction of external resources on their growth and change the fate of their original extinction. The dominant species, on the other hand, increases population size by utilizing metabolites from competing members. (2) When multiple species compete for the same limited resource, not all species can coexist. In a four-species simulation, the least advantaged species dies out and the remaining three coexist. The generation of metabolic resources by species is disadvantageous to the species itself. If the ability of species to utilize metabolic resources is the same in the simulation, the disadvantage of species in competing for external resources may not be offset. We found that when the utilization of metabolic resources in the cross-feeding relationship can make up for the deficiency of the inferior species in the competition for external resources, multiple species can all coexist. (3) We verified the universality of numerical simulation results by analyzing the influence of changes in metabolic resource-related parameters on coexistence. The results showed that the co-existence promoted by the metabolic cross-feeding relationship is insensitive to the metabolic resource related parameters, and the change of parameters only affected the population density of the species at equilibrium state. It has been found that metabolic cross-feeding relationships can promote the coexistence of competing microbial species, that is, the cross-feeding relationships among microorganisms may be a mechanism to maintain species diversity.