The utility model discloses a molding top surface square tube mounting structure, it includes: the fossil fragments unit, its fixed mounting in wall crown face, at least one side of this fossil fragments unit is seted up along its length direction's first spout, the square tube unit, its perpendicular to fossil fragments unit sets up, is provided with an at least second spout along its length direction on this square tube unit, first connecting piece, it includes the sliding part and fixed sets up on the sliding part and the joint portion of perpendicular to sliding part that this sliding part sliding connection has seted up the card hole in this joint portion in first spout, it is downthehole with the card that the second spout is worn to locate by second connecting piece, its detachably. Compared with the prior art, the utility model, under the prerequisite that need not change and customization keel structure and size, just can realize the multi -direction adjustment of square tube spare to can satisfy the furred ceiling changes or various molding demand.