The invention provides a method for manufacturing a cotton-cotton bra mold cup. The cotton-cotton bra mold cup comprises upper-layer cotton and lower-layer cotton which are adhered to each other. The method comprises the following steps: (1) respectively and independently molding the upper-layer cotton and the lower-layer cotton; (2) adhering the upper-layer cotton to the lower-layer cotton, and performing ultrasonic wave trimming for the first time; (3) turning the upper-layer cotton and the lower-layer cotton for the first time, performing ultrasonic wave trimming for the second time, and gluing uniformly; (4) turning the upper-layer cotton and the lower-layer cotton for the second time, performing overall molding shaping, and turning the edge of the shaped upper-layer cotton inwards to from a bowl opening, wherein the cutting line of the second ultrasonic wave trimmed edge is positioned on the inner side of the bowl opening. Compared with the prior art, the method can be used for manufacturing the bra mold cup which is smooth and flat in the edge of the bowl opening, is completely wrapped and is comfortable to wear, and moreover, the bowl opening edge is not easy to burst off; as the cutting lines of the ultrasonic wave trimmed edges of the upper-layer cotton and the lower-layer cotton are positioned on the inner side of the bowl opening, the bra is smooth in outer surface, free of sewing line and relatively attractive in appearance.