Sequential tracing state estimation algorithm under changed measurement triggering mode（CMTM） is presented and the concerned conceptions such as changed measurement and measurement threshold are analyzed. In this algorithm， only changed measurements are handled at every triggering moment. The problem， such as effective period for CMTM state estimation and the restarting computation， are explained via test examples. This method can not only reduce the computation time of a single state estimation， but also guarantee a fairly good estimation precision. It may have the potential of practicability.