Enhanced mutualism hypothesis considers that invasive plants promote self-growth by enriching beneficial microbial to establish positive soil feedback. However, the roles of soil microorganisms may vary with increasing time of plant growth. Here, we present results of a two-stage experiment conducted in field and greenhouse to explore the soil feedback changes with the duration growth using invasive plant Phytolacca americana L., as a model. Three P. americana individuals of varying ages were chosen based on the number of growth rings in the underground main root. We determined the effects of different growth age of P. americana on soil microbial community and physicochemical properties and performed a soil inoculation experiment to quantify the influence of microbial community structure on seed germination and seedling performance of P. americana, in the different growth age treatments. Increasing P. americana growth age altered soil properties, with significant reductions in total nitrogen (N), total phosphorus (P), nitrate-N, and ammonium-N. However increasing P. americana growth age reduced nitrogen availability in the soil; increased available potassium and available P concentrations in soil were observed in Age5 and in all growth ages, respectively. Increasing growth age influenced the soil microbial community structure, with substantial changes in the relative abundance of bacteria, including that of a few relevant to nutrient cycling; however, there was no significant change in the relative abundance of fungi. Soil inoculation experiments corroborated the change in soil microbial community structure caused by P. americana growth promoted self seed germination and biomass accumulation, which further intensified its invasion. We conclude that the early growth stages of invasive plants could promotes their growth and detailedly explained its mechanism by enrich plant growth-promoting bacteria in soil, establishing a positive nutrient cycle. When making control of invasive plants, the early detection and management should been attach importance to it.