Abstract：There are complicated folds in Paleozoic-Mesozoic sedimentary strata in the Xiluodu area along the Jinsha River. The structure resulted from superposition of three phases of folds during the Himalayan movement. The main modes of the superposition of the folds are ridden folding, shifted folding, non-sequent folding and refolding. Large-scale geological mapping and structural analysis indicate that the third-phase fold—Qingkou compound fold—constitutes a subsurface watershed, which is a barrier wall in the possible leakage path from the Xiluodu hydropower station reservoir head to the lower reaches of the Jinshan River, where karst pipe-type seepage is impossible to occur. The first determination and study of the third-phase fold in the area have great significance for the study of the leakage of the head of the huge Xiluodu hydropower station reservoir.