The invention provides a gangue-filling coal mining method for a sharp inclined coal seam under flexible shield support. The method comprises the steps of distributing working faces corresponding zones in a downhill mining mode, dropping coal by adopting an air pick, supporting the working face by using the corresponding flexible shield support to form a working space, and filling gangues above the flexible shield support through the corresponding floor tunnel along with the gradual mining operation to a coal body which is positioned below the working face, so as to enable the corresponding flexible shield support to be sunk under the dead weight and the weight of the covered gangues and form a mode of mining while filling, wherein trenches are distributed in the working faces corresponding to the zones, workers work in the trenches, produced coal is pushed to inclined coal dropping roadways corresponding to the zones by a scraper bucket and drops into a coal bunker at the underside, and then the coal is transported to a mining area through a haulage roadway after being loaded in a mine car. The flexible shield support does not need to be removed and lengthened for multiple times during mining, the filling procedure is simplified, the filling cost is reduced and the labor intensity of workers is reduced.