Abstract: To address the problem that high-end robot cables had long been dependent on imports and the requirements of million-cycle dynamic life were difficult to be met by traditional structures, the FLEX-FU 60 V 4×26 AWG+24×28 AWG flexible cable was taken as the research object, and the effect of stranding structure on dynamic bending life was investigated. Two cabling schemes were designed and compared: in scheme 1, the 26 AWG star-twisted unit was used as the central support, while inscheme 2, aramid fiber was utilized as the central filling, with the conductive cores evenly distributed around the periphery. According to the 2 PfG 2577 standard, fatigue life tests were conducted under coupled conditions of 3D torsion and bending. The results showed that the wire breakage failure caused by stress concentration in the central core of scheme 1 was effectively overcome by scheme 2; the resistance change rates of all cores were maintained below 2%, and no broken wires were observed. Furthermore, the predicted life (at the critical point of a 5% resistance increase) was reached at 9.77 million cycles, which was more than double that of scheme 1. It was demonstrated that the composite alternating stress was effectively dispersed by the application of aramid central filling, and the fatigue resistance of the cable was significantly improved. Finally, important theoretical and experimental bases for the engineering development of highly flexible robot cables were provided by the structural design principles summarized in this paper.