Creeping bentgrass (Agrositis stolonifera L.) is an economically important perennial grass species which is largely used on high value turf areas but typically show poor performance during summer months due to a lack in heat tolerance. The common symptoms induced by heat stress include photosynthesis inhibition, oxidative damage as well as interruption in metabolism, with interruption in protein metabolism, in turn, exacerbating the former two processes. To accelerate the development of more heat-tolerant cultivars, there is a critical need to better understand the intraspecific diversity in heat tolerance among different lines. Hence, this dissertation aimed to investigate heat stress mechanism in creeping bentgarss from physiology to molecular biology with a focus on protein metabolism, by studying a few promising experimental lines that have demonstrated good summer performance in preliminary trials. A broad range of thermotolerance was found to exist among different creeping bentgrass lines, with S11 729-10 identified as more heat tolerant, supported by its ability to better maintain photosynthetic capacity, regulate protein metabolism, and minimize oxidative damage. The improved physiological performance in S11 729-10 was closely associated with change in protein accumulation at various levels. At the biochemical level, S11 729-10 maintained lower activities of both protease and the ubiquitin-proteasome system (UPS), two major proteolytic pathways, contributing to its slower protein degradation and higher total protein contents. At the global protein level, S11 729-10 maintain less severe downregulation of proteins involved in the light reactions of photosynthesis, while enhancing the upregulation of antioxidant proteins, particularly during the later phase of stress. This contributed to greater cell membrane integrity and healthier light harvesting components. Additionally, at the level of ubiquitin-tagged proteins targeted by the UPS, the faster turnover of key polyubiquitinated antioxidant proteins in S11 729-10 likely represents a critical mechanism for protecting against oxidative damage and enhancing tolerance under prolonged heat stress. Taken together, this study advances our understanding of global protein accumulation and degradation though protease and the UPS, as well as their associated physiological responses, providing new insights into the thermotolerance mechanisms in creeping bentgrass. The key proteins, pathways, and unique germplasm identified in this research can be utilized for the development of new cultivars with enhanced thermotolerance to help plants cope with climate change.