A new time difference scheme which can use the data of past multi-time to determine its coefficients has been derived from the central and the forward difference used in numerical models. The computed result shows that this new scheme can improve the precision of time difference remarkably. A new time difference scheme which can use the data of past multi-time to determine its coefficients has been derived from the central and the forward difference used in numerical models. The computed result shows that this new scheme can improve the precision of time difference remarkably .