Abstract: [Objectives]　The high-temperature superconducting (HTS) D-shaped coil is one of the core components in nuclear fusion devices. It features a large operating current, high magnetic field, and significant Lorentz force, which has a significant impact on the stable operation of the magnet. Therefore, an investigation is conducted on the mechanical stability of D-shaped magnets and toroidal field (TF) coils based on the conductor on round core cable-in-conduit conductor (CORC CICC) at 20 K. [Methods]　Firstly, a three-dimensional finite element model is established and analyzed, revealing that the force per unit volume reaches its maximum at the bend of the D-shaped magnets (1.74×10⁸ N/m³) and the central section of the TF coils (2.24×10⁸ N/m³). Next, the three-dimensional thermo-mechanical coupling model is analyzed, and the mechanical stability at different positions of the magnets is studied. The quench energy and quench propagation velocity of the magnets are calculated, and it is found that both attain their highest values at the maximum magnetic field position, with quench energy measured at 1.03×10⁶ J/m3, and the axial and transverse quench propagation velocities at 142.86 mm/s and 2.77 mm/s, respectively. Finally, a method of incorporating AlN and epoxy hybrid material is proposed to improve the mechanical stability of magnets. [Results]　The minimum quench energy at the maximum magnetic field position increases. The axial quench propagation velocity is slower than that without the hybrid material, while the transverse velocity is faster than that without the hybrid material. [Conclusions]　The D-shaped magnets and the TF coils have the weakest mechanical stability points. The proposed mechanical stability method can not only effectively improve the mechanical stability of magnets, but also has significant reference value for the design and operation of large superconducting magnets operating in the 20 K temperature range.

Key words: high-temperature superconducting (HTS), conductor-on-round-core cable-in-conduit conductor (CORC CICC), D-shaped magnet, toroidal field (TF) coils, mechanical stability, quench, aluminum nitride, epoxy resin