The invention relates to a fixed device of a building composite wall body, in particular to a fastening bolt of a composite insulating wall body and a construction method thereof. The bolt comprises a screw rod and a sleeve; one end of the screw is provided with a plug with the diameter greater than the diameter of a rod body, while the other end is provided with external threads; and the sleeve is in threaded connection with the screw rod and connected with a nut. The construction method is as follows: at the intersection of a column reinforced steel rib and a beam reinforced steel rib, the screw rod passes through a preserved hole on the wall body; a second gasket is sleeved at the part of the screw rod, which is positioned in the wall body so as to lean against the binding rib of the beam reinforced steel rib; threads of the a nut are connected to the screw rod and fasten the second gasket, and the screw rod is fixed by the second gasket and the binding rib; at the positions of other column reinforced steel ribs, firstly, the sleeve is connected to the screw rod; secondly, the screw rod and the sleeve which are combined into a whole pass through the preserved hole on the wall body and pass out a preserved hole at one side of the wall body through the column reinforced steel rib; and finally, the nut is arranged for fixing the screw rod and the nut which are combined into a whole. The invention has the characteristics of simple, convenient and quick assembly, energy consumption saving, and the like.