Abstract The SSY extensometer status in Changshu seismostation from 2008 to 2011 was analyzed, through the continuous rate of the data, the noise level of the observational data and the relative mean error of M2 wave amplitude factor, the quality assessment was studied, the results show that: 1) the value of the continuous rate of extensometer is more than 99.6% in the case of no lightning; 2) the noise level and relative mean error of the M2 wave amplitude factor are in line with the deformation regulatory requirements, and they are stable; 3) SSY extensometer is mainly affected by the interference effects of barometric pressure and rainfall, and the greatest impact is rainfall.