Abstract: Three seismic stations in Chongqing area have been reconstructed. And the type of station base is changed from deep pit observation to surface observation. The PSD and PDF of the three stations before and after reconstruction were calculated respectively, and the noise power spectrum is used to average the noise curve to evaluate the background noise variation of the three stations. The calculation results show that, the environmental noise level of the three reconstructed stations still increased, especially for frequency bands above 2 Hz. The maximum increase of PSD is 9 dB at YUM station, 10 dB at LIJ station, and 4 dB at SHG station. But the overall environmental noise level between 1—20 Hz bands of the three stations still meets the requirements of the observation specifications. However, after changing the observation mode of the station base, the components of the noise signal received by the station change significantly, especially the human activity related noise. So when we carry out the construction and reconstruction of seismic stations, it is necessary to carefully change the observation mode of the station base.