High-precision free floating of test masses (TMs) is critical for TianQin, a space-based gravitational wave mission, as TMs serve as inertial references for laser interferometric measurements of spacetime perturbations induced by gravitational waves. A key challenge during TM release lies in electrostatic interactions between the TM and plungers of its grabbing positioning and release mechanism (GPRM)—exacerbated by nonideal conditions like plunger oscillation, asymmetric retraction, variable TM-plunger potential difference, and TM translation or rotation—which may degrade reference quality. To address this, a high-precision numerical model based on the finite-element method (FEM) is developed to investigate TM-plunger electrostatic coupling, with parameterized simulations via extreme-value and single-factor analyses to quantify electrostatic forces and torques on the TM and establish response models. Key results show electrostatic effects dominate along the $z$ axis due to GPRM geometric asymmetry, with the $z$-plunger more influential; plunger oscillation with maximum $2.6\mathrm{\mu }\mathrm{m}$ in the $x$ axis and $5\mathrm{\mu }\mathrm{m}$ in the $y$ axis does not exceed force thresholds, and retraction beyond $160\mathrm{\mu }\mathrm{m}$ renders plungers negligible; TM $x$-axis displacement beyond $4.76\mathrm{\mu }\mathrm{m}$ violates $z$-axis force requirements, while rotations up to 0.2 mrad about the $x$ and $y$ axes and 3 mrad about the $z$ axis stay acceptable. Under typical nonideal scenarios, TM electrostatic forces remain within TianQin’s limits, verifying the locking and release mechanism’s reliability and providing a FEM framework to support future noncontact attitude control in space-based gravitational wave detectors.

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• Classical mechanics
• Electrostatic interactions
• Gravitational wave detection
• Laboratory studies of gravity
• Space science
• Finite-element method
• Gravitational wave detectors
• Precision measurements