Abstract We regard gravity time sequence system as slow timevarying system and use difference equations for describing its equivalent parameter model based on the theory of linear systems analysis. By judging the stability of parametric sequence,we are going to explore the precursors. On the basis of gravity timevarying series from 1994 to 2009 of three observation points in Hexi gravity survey network, we prove that this method is effective, but more research are required to confirm the relations between unstability and seismic precursor anomalies.
