For the maintenance of large generators, deploying robots within the narrow air gap between the stator and rotor significantly improves efficiency and cost-effectiveness compared to traditional methods requiring rotor removal. Among various actuation mechanisms, cable-pulling robots with non-contact inspection capabilities have shown strong potential in practical applications. However, cable sag caused by gravity can lead to path deviations, which result in positioning errors and undetectable areas. To address this problem, a position compensation method based on flexible cable simulation is proposed. By employing finite element modeling of the robot-cable system, the method can dynamically adjust cable anchor points to compensate for the robot’s position deviations. Additionally, a Compensation Feasibility Map is introduced to visualize compensation difficulty across different regions inside the generator. Simulations of three generator models validate the method’s effectiveness and generalizability. The impact of key parameters—such as inspection length, air gap width, and cable pretension—on compensation performance is also analyzed, which offers theoretical guidance for practical implementation.