Tundish of small square billet continuous caster and mounting method of slag dam of tundish

The invention discloses a tundish of a small square billet continuous caster. The tundish is strip-shaped on the whole, wherein a plurality of casting holes are sequentially formed in the tundish in the length direction; dams are arranged between the casting holes; an impact area is arranged in the tundish; a slag dam is arranged in the impact area; both the slag dam and the impact area are arranged in the middle area of the tundish; the slag dam comprises a vertical main wall body and side wall bodies bending and extending from two sides of the main wall body; the cross section of the slag dam is U-shaped; a straight hole and a first flow guiding hole are formed in each of the side wall bodies; the first flow guiding holes are inclined holes, and the included angle between each first flow guiding hole and the horizontal plane is 10-45 degrees; the first flow guiding holes are obliquely and upwardly arranged from the inner side to the outer side in the thickness directions of the side wall bodies; and the straight holes are horizontally arranged.