Potassium (K) plays important roles in plant growth and development processes, while low K (LK) stress inhibits plant growth by altering reactive oxygen species accumulation. Arbuscular mycorrhizal fungi (AMF) promote nutrient absorption and transport in plants. However, the roles of AMF in affecting K nutrition are less well studied than those of other nutrients, especially in wheat. In this study, the effects of AMF on four wheat varieties were evaluated; results showed that the inoculation with the AMF-Rhizophagus intraradices significantly increased mycorrhizal colonization, fresh and dry weights, ascorbic acid, and glutathione contents, while decreasing malondialdehyde contents under both normal and LK stress treatments. It is worth noting that the contents of K and several nutrient elements were more significantly increased in roots than in shoots, suggesting that AMF mainly affect the uptake of K and other nutrient elements in the roots. Moreover, the expression levels of K transporter genes were higher than those of nitrogen and phosphorus transporter genes, especially under AMF combined with LK stress treatments. These results indicate that AMF improves wheat growth and antioxidant activity by regulating K transporter gene expression and affecting K uptake and transport. Therefore, AMF could be used as a sustainable agricultural alternative in wheat under LK soils.