Aims <p>Plant antioxidant defense is crucial for its survival in abandoned tailings with multi-heavy metal pollution. However, the tradeoff between above- and belowground oxidative defenses under multi-heavy metal risks remains unclear.</p> Methods <p>To test the changing patterns of the above-belowground tradeoff, we studied a thirty-year abandoned tailing and focused on the dominant species <i>Miscanthus floridulus</i>, a pioneer plant in remediating heavy metal polluted sites. We evaluated soil heavy metal risks, compared 10 defense traits for above- and belowground parts of <i>M. floridulus</i> across three sites along the heavy metal contamination gradient, analyzed the tradeoff and influencing factors, including plant oxidative damage and metal contents, soil biochemical property, and rhizosphere microbial diversity.</p> Results <p>We found that defense traits of<i> M. floridulus</i> had various responses in aboveground or belowground parts under soil heavy metal risk. The above-belowground tradeoff analysis indicated that the direction of tradeoff shifted from belowground to aboveground with increasing soil heavy metal risk, and the magnitude of tradeoff was the highest at the highest soil risk. The tradeoff was negatively correlated with soil aluminum (Al) content, plant belowground Al, plant aboveground magnesium (Mg), and rhizosphere microorganism’s bacterial phylum Chloroflexi, and positively influenced by soil potential ecological risk index (PERI), Cd risk (RI_Cd) and ferrum (Fe) content, plant calcium (Ca), aboveground Al and Fe contents, and rhizosphere microorganism’s bacterial phylum Proteobacteria, fungal’s phylum Basidiomycota.</p> Conclusions <p>Our results provide new insights into the defense mechanism of <i>M. floridulus</i> under soil risk from the above-belowground tradeoff perspective.</p>