In order to solve the problem of stable trapping of particles in optical tweezers in vacuum, experimental research on parameter feedback cooling of nanoparticle's center?of?mass motion was conducted. In a single beam vacuum optical tweezers system, stable capture and equivalent cooling of SiO₂ particles with a diameter of 200 nm under 3 mPa pressure were successfully achieved. Several methods for equivalent temperature estimation were compared, including the integral method using the extension based on the fitted power spectral density curve（PSD）, the integral method using the truncation based on the fitted PSD curve, and the integral method using the truncation based on the real PSD curve. The last method was selected to evaluate the equivalent cooling temperature of nanoparticles. The experimental results show that the equivalent temperature of the nanoparticle's center?of?mass motion in single axis is cooled to approximately 390 mK in minimum, and the corresponding thermal noise limit can be reduced to about 3.6% of its original value in the ultra?weak force measurement. The research results provide valuable references for the ultra?high sensitivity measurement of physical quantities based on optical tweezers in vacuum.