The utility model discloses an expanding assembly ware in semi -automatization for butt joint of pipe fitting elbow, including rotational connection means (4) that multisection universal coupling connected gradually, the front end of rotational connection means (4) passes through the frame support body and has fixed one two pole pneumatic cylinder (2), the two piston rod of two pole pneumatic cylinders props up interior bloated mould (3) of having pushed up one button head form respectively, the front end of frame support body has linked firmly one two pole pneumatic cylinder (1), the two piston rod of two pole pneumatic cylinders props up the location mould that has pushed up the one and had circular arc outer terminal surface respectively. The utility model discloses whole circle is carried out to the pipe end pointwise to the mode that expands pipe and the elbow of butt joint in by the hydro -mechanical when the assembly, with unfitness of butt joint control in standard range, and then satisfy the requirement of pipe assembly quality, guarantee the root of weld quality that takes shape, improvement assembly efficiency. The utility model discloses can effectively solve the wrong limit phenomenon that the pipe produced when the assembly, guarantee the shaping quality of root of weld, improve the production efficiency and the assembly accuracy simultaneously.