As an important structural member in self-supporting concrete floor during construction, encased steel truss-concrete composite beam has brilliant prospect in outer-jacketing structures for adding stories or mega frame structures. Compared with encased angle truss, encased round steel tube truss can facilitate layout of itself in column and facilitate layout and anchorage of prestressed reinforcement placed horizontally. N-joint is wildly used in encased steel truss. For cave-in failure easily occurs in hollow steel-tube joint, the idea that the chord is grouted to increase cave-in bearing capacity of hollow tube is proposed. Test results of 8 grouted-roundsteel-tube N-joints from the beginning of loading to failure are reported. Mechanical property and failure mode of this kind of truss joint are analyzed, and the formulas of ultimate bearing capacity of the joint corresponding to different failure modes are established. All these can provide basic data for spreading encased steel truss-concrete composite beam.