Space-based gravitational waves (GW) detection requires the residual noise spectral density of the inertial sensors to reach \(10^{-15}\textrm{m}\cdot \textrm{s}^{-2}\cdot \textrm{Hz}^{-1/2}\) from 0.1 mHz to 1Hz. High-precision torsion pendulum serves as the primary apparatus for ground test of inertial sensors. The horizontal vibration on the ground is the main noise sources for the inertial sensors tests for space-based GW detection. To reduce the ground noise, horizontal vibration is usually suppressed through the suspension magnetic damper (SMD). In this paper, a trifilar suspension magnetic damper (TSMD) is proposed to optimize the SMD in the traditional torsion pendulum. For a high-mass load, it can achieve a larger torsional stiffness without affecting the horizontal vibration isolation. Experimental results for our pendulum show that the torsional frequency of the TSMD reaches 1.237(3) Hz, and the torsional stiffness \({k_{s3}}=205.40(60)\times 10^{-3}\,\textrm{N}\cdot \textrm{m}\) , which is about \(\approx 187\) times higher than the torsional stiffness of the SMD. The motion of the structure does not affect the frequency of GW signal(0.1mHz-1Hz), effectively avoiding the non-elastic effects. The simulation results combined with experiment show that the load capacity of the TSMD is improved by 3 times compared with the SMD while the horizontal isolation capacity is similar (the swinging resonant frequency \({f_{s1}=1.182(6)\,\textrm{Hz}}\) for SMD, and \({f_{s3}=1.591(4)\,\textrm{Hz}}\) for TSMD). The TSMD provides a technical approach for ground testing of inertial sensors in space-based GW detection.
