Abstract: Maintaining river ecological flow is a fundamental requirement for ensuring the health of aquatic ecosystems, with fish being the apex species within these ecosystems. Based on ecological surveys, this study explores the ecological flow of the main channel of the Xiaoqing River in Shandong Province using a habitat simulation method. First, relative importance indices were used to select fish indicator species for different seasons. Habitat suitability curves for fish species were then drawn based on habitat surveys and relevant literature. The habitat simulation method was employed to determine the ecological flows required to meet the habitat suitability needs at three ecological flow control sections: Huangtai Bridge, Chahe, and Shicun hydrological stations. Subsequently, by calculating ecological flow guarantee rates, a comparison was made between the ecological flows obtained through hydrological methods and the habitat simulation method. In combination with navigation requirements of the Xiaoqing River, a multi-objective ecological flow was determined, balancing fish habitat suitability, hydrological rhythm, and navigation needs. A comparison with long-term observed monthly average flows at the three control sections yielded annual average guarantee rates of 98.21%, 83.77%, and 80.13%. However, the guarantee rates for June at the Chahe station and for April and May at the Shicun station were significantly below average, warranting special attention.