The invention provides a method for improving roughness of an inner surface of a crucible for a polycrystalline silicon ingot. The method comprises the following steps that slurry is prepared, specially, the slurry is put into a spraying device, wherein the spraying device comprises a rotary spray head, the spray head comprises a base and at least two gas dispersing devices arranged on the base, aslurry hole is formed in the center of the base, at least two gas dispersing devices are intersected in the slurry hole, each gas dispersing device comprises a first side wall and a second side wallconnected to the first side wall, at least two first side walls are intersected in the slurry hole, and a first dispersing hole is formed in each first side wall; and the spraying device is started, specially, the slurry is sprayed out from the slurry hole, compressed air is sprayed out from the first dispersing holes, so that the slurry is dispersed into a plurality of particles, and the plurality of particles form slurry points on the inner surface of the crucible. The slurry is sprayed out through the rotary spray head, and the slurry is dispersed into the plurality of particles through compressed air sprayed out of the obliquely-arranged first dispersing holes, the particles uniformly falls on the inner surface of the crucible so as to form the slurry points, and finally the roughnessof the inner surface of the crucible is improved.