<p>Herbaceous peony (<i>Paeonia lactiflora</i>), a high-value cut flower species in the international horticulture market, faces regional cultivation restrictions due to its susceptibility to summer high-temperature stress. Although WRKY transcription factors (TFs) are known to mediate plant stress responses, their function in herbaceous peony, particularly dimerization-mediated mechanisms, remains poorly understood. This study identified PlWRKY31, a WRKY Group IIb member, as a key regulator of high-temperature tolerance. PlWRKY31 was a nuclear-localized protein whose expression was strongly induced by high-temperature stress. Virus-induced gene silencing (VIGS) of <i>PlWRKY31</i> significantly reduced high-temperature tolerance in herbaceous peony. Under high-temperature stress, <i>PlWRKY31</i>-silenced plants exhibited more oxidative damage, including excessive reactive oxygen species (ROS) accumulation, reduced photosynthetic efficiency, and impaired membrane stability. Furthermore, the activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were significantly lower in silenced plants compared to the control. Notably, yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and dual-luciferase assays confirmed that PlWRKY31 interacted with PlWRKY72, a homologous Group IIb member. The PlWRKY31-PlWRKY72 module might positively regulate high-temperature tolerance by coordinately activating the antioxidant enzyme system and maintaining ROS homeostasis. This study not only reveals the molecular mechanism by which <i>PlWRKY31</i> regulates high-temperature response in herbaceous peony, but also provides critical insights for breeding high-temperature-resistant horticultural varieties.</p>