Abstract：Precision instrument is very sensitive to environmental ground vibrations，which may not be felt by human being but can cause malfunction of precision instrument. Four measure sections were chosen along metro line，where in-situ tests of metro and ground traffic induced vertical ground vibrations were carried out by using high sensitive accelerometers. The 350 ground vibration time-history curves of 94 records were transformed into 1/3 octave band frequency spectrum. Based on the transformation，the characteristics of ground vibrations induced by the normal operation of metro and ground traffic were investigated. Finally，the law of impacts of ground vibrations on precision instrument was discussed with reference to an electron microscope Tecnai30 for analyzing environmental vibration impacts on precision instrument. It is found that there exists an “equal vibration frequency” for ground vibrations. When the frequencies of ground vibrations are smaller than the “equal vibration frequency”，ground vibrations are mainly dominated by background vibrations，while the effect of distance is very weak；however，when bigger than the “equal vibration frequency”，it is mainly governed by distance，but the effect of background vibration is only inferior to the distance. Ground vibrations with frequency smaller than “equal vibration frequency” have higher impacts on precision instrument affected by background vibrations. When vibration frequency is bigger than “equal vibration frequency”，impacts on precision instrument decrease with increasing distance form line center. Superposition of metro induced ground vibrations and ground traffic causes the response within 6–30 Hz is found to be prone to affect precision instrument. “Equal vibration frequency” is first found in this experiment and its implication needs to be further studied.
