Abstract: A diagrid structural system is an innovative super high-rise building structural system, the key part to ensure safety and reliability is the joint that is oblique crossed by a batter post. Based on the tests and theoretical analysis at home and abroad, the structural form, mechanical performance and failure mode of planar intersecting concrete filled steel tube (CFST) connections in a diagrid structure are analyzed. Considering the restriction effect on core-concrete, the mechanical performance of core-concrete, which is in a planar intersecting joint area or not of round steel tube concrete skew grid, is analyzed based on the Twin Shear Unified Strength Theory. The compressive strength formula of planar intersecting CFST connections in a diagrid structure is proposed. Formula results are in a good agreement with test results. The result shows that the formula deduced in the paper has good applicability. Furthermore, the influence factors of bearing capacity of the joint are analyzed, and the failure mode and controlling factor of planar intersecting concrete filled steel tube connections in a diagrid structure are discussed. The mechanical performance of an elliptical connection plate is analyzed based on Von Mises yield criterion, and a critical angle formula is proposed. Research findings have an important practical value.