To study the seismic behavior of concrete-filled square steel tubular column to U-shaped steel-concrete composite beam joints with separated internal diaphragm, four joint specimens were tested under cyclic loading. The test parameters are the diaphragm type and the connection forms at the beam-column interface. The hysteric behavior, ductility, energy dissipation and deformation were analyzed and suggestions the designing the reinforced plate were provided. Test results indicate that the beam bending failure occurred in all specimens, and the hysteric curves show an inverted S-shape, with an obvious pinch effect. The displacement ductility coefficient ratio is between 2.3-3.1, the elastic limit of inter-story drift rotation is between 1/68-1/53, the elastic-plastic limit of inter-story drift rotation is between 1/28-1/19, and the equivalent viscous damping coefficient is between 0.12-0.16, indicating that the specimens show good deformation and energy dissipation capacities. Changing the type of diaphragm has little effect on the load-carrying capacity of the specimen, but compared with the traditional internal diaphragm joints, the energy dissipation capacity of the weak axial internal diaphragm joints is decreased. Strengthening the beam-column connection can alleviate the stiffness degradation and effectively improve the bearing capacity and energy dissipation capacity of the joints.