Aiming at the composite spoiler joint of a certain aircraft， the typical cross joint area is selected as the research object to study its ultimate load bearing capacity of the RTM （Resin transfer moulding） formed composite spoiler joint under the four point bending load. Its damage and failure mode is analyzed， and a reference for the design of RTM formed composite joints is provided. A finite element model of the typical detail of the cross connection area is established and its damage process is simulated using the commercial software ABAQUS. The simulated results agree well with the experimental data and thus the feasibility of the numerical simulations is verified.