Abstract: The tide analysis method was used to analyze and assess changes in the quality of the observed data before and after the renovation of cavern with vertical pendulum tiltmeter in Malingshan seismic station. The results show that: ① The observation accuracy （m_γ） of every year all is less than 0.02, it has a markable improvement after the instruments relocation, which is better than before, surpassing the standard of excellent deformation stations of the whole country. ② After the relocation, the noise level （M₁） is always around 0.005″, and the stability is better. ③ After correction, it is found that there is a large deviation in the installation azimuth of the instrument before relocation, which affects the phase lag of M₂ wave. Optimization of chamber environment is beneficial to improve the accuracy of observation data, and it provides a guarantee for the observation equipment to produce high-quality observation data.