The invention relates to a warning method for a widened area on the inner side of a small-radius curve to improve road safety. Firstly, the widened area of the small-radius curve is divided by setting out; secondly, the road surface of the widened area is colored and is paved with colored anti-slip materials; thirdly, marked lines are coated on the road surface of the widened area, an edge line of a roadway on the inner side of the widened area is covered with yellow solid marked lines, the outer side of the widened area is painted with white dotted marked lines, zebra crossings and vehicle stop lines in the widened area are normally constructed, and other portions of the inner side of the widened area are marked with oblique lines or serrated white marked lines; and finally, warning signs are arranged on a sidewalk or a green belt on the inner side of the widened area, and curve pedestrian warning sign layers are arranged on double surfaces of each warning sign. By the aid of the marked lines arranged on the widened area and the signs arranged on the sidewalk or the green belt on the inner side of the widened area on the inner side of the small-radius curve, safety of pedestrians, bicycles and motorcycles passing through the widened area on the inner side of the small-radius curve is improved.