The utility model discloses a sliding type first slag stopper for the tapping of a converter. The sliding type first slag stopper comprises a deformable cylindrical fiber drum with an inner cavity and an expansion siding block positioned in the inner cavity, wherein a first pulling hole is formed in the bottom of the cylindrical fiber drum; a second pulling hole coaxial with the first pulling hole is formed in the center of the expansion sliding block; and the outer surface of the expansion sliding block is in close sliding fit with the inner cavity. The utility model has the advantages that the sliding type first slag stopper for the tapping of the converter is simple in structure; the cylindrical fiber drum is extruded outwards through the expansion sliding block to increase the diameter of the cylindrical fiber drum, and is clamped in a tapping hole, so that the shortcoming of expansion hysteresis in the background art is overcome; and in addition, the sliding type first slag stopper is low in cost, and has good economic benefits.