The circular hollow section (CHS) has lots of advantages in excellent structural properties, architecturally attractive features. Thus, CHSs are used extensively in many applications in buildings, bridges, towers, and offshore. In CHS, it is necessary to understand the various complex shape of CHS joint because loads act simultaneously according to joint type. The use of high-strength steel has been continuously increased, but the current design equation in AISC 2011 or KBC 2016 limits maximum yield strength 360 MPa. This paper studies an interaction strength of high-strength CHS-to-longitudinal plate X-joint subjected to combination of plate axial load and in-plane bending moment. For the study, numerical analysis based on experimental tests was carried out. The analysis was performed according to variables for determining shape of joint, i.e., chord slenderness, plate width-to-CHS diameter ratio, and utilization ratio. Investigations have shown that a linear summation of the ratios for axial load and in- plane bending moment may be used as conservative approximation.