This work proposes a square concrete-filled steel tubular (CFST) joint system, in which vertically placed diagonal plates help transfer the tensile load from the beam flanges. The CFST diagonal-plate connections were experimentally investigated under tension. The failure mode was analyzed based on the test results. The CFST diagonal-plate connections achieved the beam end failure mode, and the stress concentration at the steel tube corners obviously relieves. The Void Growth Model (VGM) model was used to predict the fracture of each specimen, and it showed high accuracy compared with the experimental results, which verified the applicability of the VGM model for predicting the entire process of forces of the CFST diagonal-plate connections under tensile load. Component-based models have been developed and used for predicting the initial stiffness and strength of the CFST diagonal-plate connections. The hand calculation procedures for yield and ultimate deflection were also developed. The load–deformation curve consists of three segments: the first represents the elastic behavior from the classic plate theory, the second is obtained by plotting the deformation at the ultimate strength against the maximum load, and the third is a horizontal line stretching to the failure point. The mechanical models were compared with test and numerical simulation results, and good agreement was shown between them.