A sectional lighting fixture structure includes a hollow main body, an end cap connected to and closing a rear open end of the main body, a socket connected to an inner side of a front open end of the main body for a bulb to mount thereto, and a lighting lampshade externally connected to the front open end of the main body. The main body is a lightweight metal cylindrical body having been subjected to expansion process to include two straight walls at the front and rear ends, and a middle portion having a plurality of bellow expansion joints that provides the main body with good pressure resistance. The socket is in the form of a heat-resistant insulating wool, so that heat produced by the bulb mounted thereto is not transmitted to the main body to adversely affect a normal temperature of a ballast mounted in the main body.