The utility model discloses a side core-loosening device for a mould, which comprises a lower template and an upper template. At least one containing groove is arranged at the joint face of the lower template in a concave manner, and a mould cavity unit is respectively arranged in each containing groove. Each mould cavity unit comprises two positioning pieces, a plurality of first inlaying pieces, two second inlaying pieces, two controlling pieces and two positioning rods. Top-leaning springs are respectively arranged between the containing grooves and the positioning pieces. The side core-loosening device for the mould can be used for producing a medical hair brush.