The inereasing amount of municipal sludge poses a serious threat to the environment. Traditional treatment methods still face various challenges in terms of harmlessness and resource utilization. Hydrothermal carbonization is considered an effective method for treating municipal sludge, but its low carbon and high ash characteristics limit the application of hydrochar as a fuel. To address this issue, the co-hydrothermal carbonization of municipal sludge and enteromorpha (a high-carbon and low-ash waste biomass) is proposed as a potential solution. In this study, co-hydrothermal carbonization experiments of municipal sludge and enteromorpha were conducted under various reaction conditions, including temperatures ranging from 160 to 280 ℃, residence times ranging from 30 to 150 minutes, and municipal sludge proportions ranging from 0% to 100%. The impacts of these process parameters on energy recovery efficiency (ERE) and electricity consumption index (ECI) were investigated. The response surface method was adopted to optimize the three main factors (temperature, time, and municipal sludge proportion) affecting ERE and ECl. The results indicated that the response surface models established by Central Composite Design exhibited a good fit (model P<0.05, corresponding="" lack-of-fit="" p="">0.05), with minimal deviation between predicted values and actual values. Municipal sludge proportion had a significant impact on ERE (P<0.05), while="" time="" exerted="" an="" extremely="" significant="" influence="" on="" eci="">