In the Taiji project—a Chinese space-borne gravitational wave detector—the Drag-Free and Attitude Control System (DFACS) is the core technology responsible for maintaining the inertial motion of the test-mass (TM). A thorough understanding of the spacecraft (SC) dynamic behavior under complex gravitational perturbations and multi-source non-gravitational disturbances is crucial for optimizing control system design, studying data processing pipelines, and verifying the detector performance. In this paper, we propose a unified simulation framework integrating the constellation orbital motion with a full-state closed-loop DFACS system for the first time and develop a 60 degrees of freedom (DoFs) DFACS simulator. Furthermore, benefiting from the introduction of high-precision numerical methods, the simulator is extended to 31 significant digits, which supports high-fidelity numerical simulation of the inter-satellite laser interferometry measurements from picometers to million-kilometers. Three different experiments are implemented to assess the performance of DFACS via analyzing the single TM’s residual force noise, moving optical subassemblies (MOSA)’s jitter, and the arm-length variation of TM-TM and SC-SC. Moreover, we quantitatively demonstrate the feasibility of decoupling DFACS design and orbit optimization. For the Taiji project, this study enables a more realistic on-orbit simulation of the detector and provides a representative system response under closed-loop control, supporting more accurate detector sensitivity analysis and facilitating refined optimization for scientific objectives.