Comprehensive water cut of Sa-er-tu reservoir of Ying-tai oilfield in Jilin is over 92%. Under the background of improving well oil rate, formation sensitivity to injected water, potentiality of infill drilling, residual oil distribution, oil recovery factor, abundance of oil in place, as well as the relationship between reservoir heterogeneity and producing performance have been evaluated objectively by integrated employing fine reservoir characterization, experimental methods, reservoir engineering theory and numerical simulation techniques. Two reservoir concepts, ‘Degree of oil gathering in a layer’ and ‘Degree of oil in a single sand body’ have been first put forward to quantify the shift of development contradiction from inner-layer to inner-sand body and the geological tendency of plugging the high permeability band in a sand body respectively. Our findings are of significance to correct understanding the water flooding effects of Sa-er-tu reservoir of Ying-tai oilfield and to making clear the adjustment measures to be adopted to improve oil recovery.