Abstract: A light gauge steel joist basic structure system of a light partition wall is disclosed, comprising: top and ground joists and vertical joists. The top and ground joists comprise a ground joist and a top joist. The vertical joist is provided between the top and ground joists by means of a first connection member. The vertical joist and the vertical joist are fixedly connected to each other by means of the first connection member and/or a second connection member. V-shaped slots are symmetrically provided on two side walls of the top and ground joists. The V-shaped slots are provided on the side walls and the bottoms of the vertical joists. A construction method for a light gauge steel joist basic structure of a light partition wall is also disclosed. The light gauge steel joist basic structure system is simple and fast to be constructed and has desirable flatness.