A structural steel member connecting assembly includes a first connecting member and a second connecting member. The first connecting member is pivotally connected to a positioning portion of a first structural steel member and therefore can be swung. The second connecting member is pivotally connected to the first connecting member such that the two connecting members are rotatable with respect to each other. The second connecting member has a fixing portion coupled with a second structural steel member such that the longitudinal directions of the two structural steel members intersect. With the second connecting member rotatable with respect to the first connecting member, the installation angles of the two structural steel members can be easily changed in order to make a stable engineering structure. The structural steel member connecting assembly features convenience of, and flexibility in, use and has extensive applications.