An illumination lamp having a light-projecting angle adjusting function includes: a base unit, a light-emitting unit and a retaining unit. The base unit includes a retaining module, and the retaining module has a plurality of retaining grooves arranged as a surrounding shape and a surrounding receiving groove. The light-emitting unit is disposed on the base unit. The retaining unit includes a movable retaining element penetrating through the light-emitting unit and moved along with the light-emitting unit. In addition, the movable retaining element has a first end portion and a second end portion corresponding with each other, and the first end portion selectively positioned in one of the retaining grooves for positioning the light-emitting unit or movably disposed in the surrounding receiving groove for rotating the light-emitting unit.