Parallel-wiring cables are often used in multi-phase AC aircraft Electrical Power Systems (EPSs). However, it complicates the ac resistance estimation. To solve this issue, an analytical resistance calculation method for parallel-wiring cables in multi-phase EPS was proposed. Firstly, the existing calculation formula of proximity factor was optimized, and the calculation error was reduced from 16% to 2% when two conductors are close to each other. Afterwards, the superposition effect on current density distribution between multi-conductors was considered based on orthogonal decomposition method, and the position of the equivalent charged points were easily determined. Finally, the ac resistance calculation formula was derived according to characteristics of parallel-wiring strategy, and the general ac resistance calculation methods of multi-phase parallel-wiring cables were presented. The proposed approach considerably enhances the applicability of ac resistance analytical calculation method for multi-conductor cables. Thanks to the accuracy of the proposed method, it can be used in many cases to avoid case-by-case simulation work and facilitate efficient system design and analysis.