The invention discloses a method for determining side slope dangerous rock body stability in a water-power engineering environment, and relates to water-power engineering. The method for determining side slope dangerous rock body stability in the water-power engineering environment meets water-power engineering practice and is beneficial for reducing unnecessary side slope dangerous rock body treatment. The method determining the side slope dangerous rock body stability in the water-power engineering environment includes the steps that according to the level of a hydraulic structure affected by an environment side slope dangerous rock body, the area of the affected hydraulic structure and whether the area of the affected hydraulic structure is a crowded engineering activity area or not, the estimation level of dangerous rock body stability is determined, stability of key portions of the hydraulic structure and safety of the crowded engineering activity area are ensured, the stability estimation standards of non-key portions and non-crowded engineering activity area are reduced, an environment side slope is distinguished to the maximum, and the method is beneficial for reducing unnecessary side slope dangerous rock body treatment, avoids unnecessary engineering investments and saves the construction period.