Reinforced Concrete column and Steel beam (RCS) structural system has been extensively studied due to the effective use of concrete and steel material and cost efficiency. Bearing failure and constructability were two main issues of RCS joint in practical engineering. To improve these two deficiencies, the authors proposed a whole-section diaphragm type RCS joint. This study aimed to examine the impact of axial compression ratio and face bearing plate (FBP) thickness on the seismic behavior of the proposed joint. In this research, six RCS joint specimens were designed to achieve joint failure and tested under cyclic loading. Shear failure was identified as the typical failure mode. The results revealed that higher axial, compression ratio could lead to higher cracking loads, with improved load-carrying capacity, stiffness, and energy dissipation capabilities. Additionally, the joint bearing distortion reduced as the axial compression ratio increased. All specimens displayed spindle-shaped hysteresis loops while the specimen without axial compression exhibited pinching effect. The presence of parallel FBPs significantly improved the shear capacity. However, as the thickness of the parallel FBPs increased from 6 mm to 10 mm, the load-carrying capacity showed limited enhancement. Moreover, a comparative analysis of current calculation methods was conducted. The results demonstrated that the AIJ and CECS347:2013 formulas showed acceptable accuracy in predicting the joint shear strength. These findings validated the applicability of the existing methods for proposed composite joints, while the effect of the axial compression ratio required further evaluation.