In the processing of seismic data from western China, there frequently exists a residual static time difference of tens of milliseconds after elevation and datum corrections. In the stacked profiles, the effects of this static time difference on the shape of the reflection undulation are different in shallow, middle and deep layers, i.e., there exists the phenomenon of "non-static statics". An analysis shows that such a phenomenon is attributed to high stacking multiplicity and large offset in the arrangement. For the shallow, middle and deep layers in the same CMP gather, the number of the traces participating in stacking is quite different, which causes different smoothing actions during stacking on the static time difference. Different from the "non-static statics" phenomenon caused by different propagation paths of the reflection in mountain areas, it remains "surface consistent". The correct analysis of the cause of this type of phenomena provides a basis for the correct application of static correction.