The invention provides a calculate method applied to a fault basin steep hill with fan body top surface variables. The method includes that overlying strata cumulative gap H is calculated after deposition of a fan body by using three dimensional seismic data, actual drilling data and speed data; cumulative geological time Delta T based on a geological time scale after deposition of the fan body iscalculated; fault true dip Alpha is determined by a two-dimensional section which is vertical to the fault direction; the gap, deposition time and fault dip angle are integrated to calculated a cumulative active speed after deposition of the fan body; sand percentage composition P is calculated by using a ratio of fan body sand thickness and ground thickness and characteristic fan body top surface variables are quantized by using the ratio of cumulative fault active speed S and fan body percentage composition, fan body top surface occurrence evolution types depending on the size of the shapevariables. The method considers main influence factors of the fan body shape variables from all angles, and conducts to quantize the characteristic, has reasonable methods and wide promotion and application value.