Negative stiffness vibration isolation platform (NSVIP) is widely used in quantum precision measurement equipment such as atomic interference gravimeter. Its performance is significantly influenced by low-frequency performance and environmental adaptability of the isolator. To improve overall performance of the vibration isolator, this research performs a semi-active transformation of a standard commercial NSVIP. Firstly, the force-displacement relationship is analyzed theoretically, focusing on the determinants of negative stiffness characteristics and bearing capacity. Then, the motion model is formulated and analyzed, and the parameters are accurately identified in the time and frequency domain, respectively. Moreover, the semi-active vibration isolation ( SAVI) is simulated and analyzed, and the Bayesian optimization is used to quickly determine the optimal control parameters. Finally, the scheme is further verified on the actual system. The result shows that SAVI can attenuate the low-frequency resonance peak by 357 times. The system can achieve good vibration isolation effects in the frequency band below 0. 3 Hz and above 8 Hz. The low-frequency vibration isolation performance is significantly improved. The proposed solution can be widely used in related vibration isolation equipment for quantum precision measurement.