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, FLEX-FU 60 V 4×26 AWG+24×28 AWG flexible cable was taken as the research object, and effect of stranding structure on dynamic bending life was investigated. Two cabling schemes were designed and compared: in scheme 1, 26 AWG star quad unit was used as the central support, while in scheme 2, aramid fiber was utilized as the central filling, with conductive cores evenly distributed around the periphery. According to 2 PfG 2577/08.16, fatigue life tests were conducted under coupled conditions of 3D torsion and bending. Results showed that wire breakage failure caused by stress concentration in central core of scheme 1 was effectively overcome by scheme 2; DC resistance change rates of all cores were maintained below 2%, and no broken wires were observed. Furthermore, predicted life (at critical point of a 5% DC resistance increase) was reached at 9.77 million cycles, which was more than double that of scheme 1. It was demonstrated that composite alternating stress was effectively dispersed by the application of aramid central filling, and fatigue resistance of the cable was significantly improved. Finally, important theoretical and experimental bases for engineering development of highly flexible robot cables were provided by structural design principles summarized in the paper.