Abstract: The exterior joint of the steel-bamboo composite I-section beam and box columns is constructed through T-stub and bolts and strengthened by steel tubes with steel plate welded around the core of the connection to improve the joint region’s stiffness and overall performance. Taking the number and the strength of the bolts as variables, quasi-static tests were performed on 6 composite beam-column exterior joints with or without stiffeners to evaluate the P-Δhysteretic curves of the joints, the rotation between beams and columns and the shear deformation of the steel plates welded to the core of the connection. The dissipative coefficient, ductility, and other anti-seismic parameters of the composite beam-column exterior joints were derived, based on which, the theoretical calculation methods of the rotation at the connection were analyzed. The result shows that the strength and the number of the bolts have little effect on the shear deformation at the core and the ultimate load capacity of the joints, but changes of stiffener and weld size of the steel tube have obvious influences on the rotational stiffness and anti-seismic parameters. Based on the displacements at the ends of the beam and the stress-strain curve within elastic range of the steel-bamboo composite joint, the simplified mechanical model and the method to calculate the rotation of the connection were proposed in this paper. The theoretical results matched well with the experimental values.