The high fill slope formed during the construction process of power plants is one of the dangerous sources that threaten the safety of power plants. Comprehensive analysis of high fill slopes is helpful to understand the universal laws of slope instability, and provide theoretical basis for similar slope treatment. The deformation mechanism and reliability of prevention and control measures of high fill slopes in a power plant in Indonesia are comprehensively explored through geological survey, stability evaluation, numerical simulation, and long-term monitoring. The research results show that the failure mode of high fill slopes mainly revolves around weak structural planes, such as sliding or uneven settlement of surface fill and coal seams. Prevention and control measures such as slope protection system and reinforcement grid inside the slope can effectively improve the stability of high fill slopes. Long term monitoring is an important basis for evaluating the reliability of slope reinforcement, and also an important means for early evaluation of potential hazards in slopes.