We use the 2011～2018 data of 260 continuous Global Positioning System(GPS)stations to study CME of China. The PCA method is used to conduct regional common-mode error analysis on the obtained residuals time series which is after deduction of deformation signals such as tectonic movements. The PCA method has proved to be an effective tool to estimate the CME at continental scale. Space-time filtering of position time series with the results of the PCA significantly improves the signal-to-noise ratio. The CME in the study region contained within the first two PCs,the spatial distribution of the first principal component is uniform,and the spatial distribution of the second principal component presents an obvious gradient change pattern,which suggests that the second principal component is not a local effect of a few stations,but is a supplement and correction to the first principal component. The second PCs should not be ignored for the CME analyses of our country. By comparing the common mode errors of the residual time series of the constant amplitude seasonal term and the modulated amplitude seasonal term,we found that CME which consider amplitude modulated significantly weakened the characteristics of the annual cycle,indicating that the un-estimated “signals” which are ignored when time series analyses will be evolved into CME,revealing that common mode errors,including signals and errors,are not simply errors.