The utility model relates to a lower slide brick of a sliding mechanism for steel mould casting. The lower slide brick is arranged between a middle slide plate and a water outlet port; a lower slide brick body is provided with a flow guidance groove with a certain inclined angle in the water port closing direction of the middle slide plate of a sliding mechanism; and one side of the low guidance groove is communicated with a molten steel hole of a lower slide plate. According to the utility model, the flow guidance groove with a certain inclined angle, which is connected with the steel flowing hole of the lower slide plate, is designed on the upper plane of the lower slide brick of the sliding mechanism along the water port closing direction of the middle slide plate; and molten steel remaining in the steel flowing hole of the lower slide plate can be introduced to the flow guidance groove to flow away along the water outlet hole in the water closing process of the middle slide plate after the drainage of the molten steel, so that the molten steel can be prevented from being cooled in the steel flowing hole of the middle slide plate to block the water port so as to realize the multiple-time interrupted casting.