The cable-driven snake arm maintainer (SAM) simplifies the electronics of the entire snake arm and is well suited for operation in narrow and high-risk environments. However, the structural features of the SAM, the large slenderness ratio and the effects of variable loads and rigid-flexible coupling deformation lead to large end position error. In order to improve the positional accuracy, a joint space error compensation model of a SAM is constructed using the matrix differentiation method. The error parameters under different loads and different poses are identified based on the principles of variable parameter error compensation and a linearized variable-load variable-parameter model. Parameter errors are then calculated by the Levenberg-Marquardt nonlinear damped least-squares algorithm. Finally, we verify the effectiveness of the proposed algorithm by simulation and error compensation experiments. The results of the study provide a theoretical basis for further accuracy improvement and application expansion of the SAM.