The utility model provides a door buttress that is used for shear force wall side housing door opening in a wall mouth prefabricated installation, includes two at least components, is equipped with the elasticity piece on being located the top surface of the component at top, is located the subaerial elasticity piece that also is equipped with of the component of bottom, each component distributes along the direction of height in proper order, the component includes the concrete piece built -in fitting inside with locating the concrete piece, be equipped with the mounting groove with external intercommunication on the concrete piece, the built -in fitting sets up along concrete piece direction of height, the built -in fitting includes vertical pre -embedded steel bar and sets up the horizontal pre -embedded steel bar on vertical pre -embedded steel bar, pre -buried steel sheet and brace rod, vertical pre -embedded steel bar sets up along concrete piece direction of height, additionally, horizontal pre -embedded steel bar and pre -buried steel sheet all set up along concrete piece width direction, are equipped with the perforation with the mounting groove intercommunication on the pre -buried steel sheet. The utility model discloses a prefabricated door buttress, made things convenient for door buttress quality the accuse, improved construction speed, reduce raw and other materials extravagant, reduced construction cost simultaneously.