The invention discloses a positioning device of an L-type building decoration wall surface. The positioning device comprises a hook and a connector fixed to the hook. The connector is of an L shape composed of a transverse plate and a vertical plate. A trapezoid groove is formed in the top of the hook. The connector is detachably fixed to the upper portion of the trapezoid groove in the top of thehook through a bolt assembly. A bolt head portion of the bolt assembly can slide along the trapezoid groove before the connector is fixed. The vertical plate of the connector is provided with an elliptical groove hole capable of being adjusted vertically. In this way, the adjustment of the installation position of a house external wall face plate is realized, the deviation of the installation position between the face plate and a supporting keel is eliminated, and therefore the installation and detachment of the face plate are facilitated.