Objective: The low-gravity simulation test platform serves as a pivotal and indispensable component of facilities dedicated to spacecraft landing and takeoff verification. Considering the rapid diversification and increasing complexity of modern aerospace missions—including crewed lunar landings, Mars sample return, and deep-space exploration—the need for in-depth research on digital design methodologies for low-gravity simulation systems tailored for manned lunar modules has reached an unprecedented level. Equally critical is the construction of ultralarge-load low-gravity simulation test facilities capable of meeting the stringent technical demands of next-generation heavy-duty spacecraft. However, a prominent theoretical bottleneck persists in the current research landscape: a complete and accurate theoretical description of the force—displacement characteristics of core mechanisms, such as parallel cable drives in low-gravity simulation test platforms, remains elusive. This bottleneck limits the understanding of key performance parameters and characteristics of parallel cable drive systems. Examples include torque transmission efficiency, displacement response characteristics, and the intricate correlations of performance parameters with environmental interference factors (e.g., temperature fluctuations and ground vibrations) and variable load conditions. Consequently, practical guidance for engineering applications remains limited and fragmented. This hinders further improvement in position and force control accuracy during spacecraft low-gravity simulation tests and in the precise design of future ultralarge-load low-gravity simulation test platforms, such as those required for landing and takeoff validation of manned lunar modules. Methods: To address major national strategic needs, such as the construction of specialized low-gravity simulation test platforms for manned lunar modules, this study focused on the core technical challenge that the force-displacement characteristics of parallel cable drive systems in low-gravity simulation test platforms are difficult to predict and control. First, a rigorous, systematic force—displacement characteristic model of the parallel cable drive system of a three-dimensional servo platform was established, covering the full effective workspace. This model incorporated key influencing factors, including cable elasticity, geometric layout constraints, and dynamic coupling between the servo platform and the payload. Furthermore, a high-fidelity model for simulating the multibody dynamics of the parallel cable drive system was developed using MATLAB/Simulink. The simulation model reproduced the physical model of the parallel cable drive system with a strict 1∶1 ratio and was composed of 18 independent cable drive mechanisms. These mechanisms were categorized into three subsystems: upper, middle, and lower diagonal cable systems, each responsible for controlling specific degrees of freedom of the servo platform. Results: Using the established simulation model, researchers could accurately simulate real three-dimensional working scenarios related to typical spacecraft operating conditions, such as high-dynamic landing with variable impact loads and ignition takeoff with thrust vector control. The model enabled comprehensive quantitative analysis of multiple critical performance indicators, including the real-time motor motion state (position, velocity, acceleration, and torque output) of the parallel cable drive system, dynamic motion trajectories and tension distribution characteristics of each cable in the parallel cable drive system, and directional stiffness of the cables at any arbitrary position within the workspace. Conclusions: This study fulfills two major objectives. First, it enables rapid identification of the root cause of reduced positioning and speed control accuracy in lunar surface detectors during low-gravity simulation tests. This, in turn, provides targeted technical guidance for the detectors to conduct a full range of comprehensive verification tests—such as hovering stability, obstacle avoidance maneuvering, and controlled slow descent—on the low-gravity simulation test platform. Second, the established theoretical model and simulation framework offer a solid theoretical reference and technical support for the design of future ultralarge-load low-gravity simulation test platforms, such as those intended for manned lunar modules. This lays the foundation for the successful implementation of subsequent deep-space exploration missions.