Arbuscular mycorrhizal fungi (AMF) play important roles in the dynamics of soil organic carbon (SOC), as they can promote its accumulation and the formation of soil aggregates, thereby increasing soil carbon storage. However, the impact of carbon input through AMF inoculation on SOC sequestration is still unclear. In this study, the effects of AMF on photosynthetic carbon transport and SOC accumulation in two types of black soils with either high or low SOC soils were analyzed by an outdoor pot experiment using isotope ¹³C labeling, thus, revealing the mechanism of action of AMF in stabilizing SOC fixation. The results showed that AMF symbiosis increased the allocation of photosynthetic carbon to the roots of the maize plant and soils. Inoculation with AMF also increased the proportions of soil macro-aggregates and the soil microbial biomass carbon content in low SOC soil, promoted the accumulation of soil aggregates, and enhanced the chemical composition of SOC. After returning the harvested labeled straw to the original pots the following year after planting, inoculation with AMF was found to increase the contents of hemicellulose and lignin at the time when maize kernels attained a plump appearance. AMF significantly increased glomalin-related soil protein in high SOC soil. In addition, AMF had a promoting effect on the decomposition of cellulose, hemicellulose, and lignin in the straw, which could subsequently increase the accumulation of carbon. We provide evidence for the promotion of soil aggregates, soil C accumulation, and SOC sequestration with AMF inoculation.