Abstract: The producing degree of main reservoirs in Wen chang A oilfield was close to or bigger than the oil displacement efficiency of short core testing and it was unable to carry out the reservoir simulation study of remaining oil.Therefore,new understandings on displacement efficiency of main reservoirs needed to be known so as to provide guidance for remaining oil distribution and potential analysis.Based on the oil displacement efficiency experiment of sealing cores in Wenchang A oilfield,the experiment study of oil field displacement efficiency was carried out.The experimental results indicated oil displacement efficiency in long cores was bigger than that of in short cores and application results were more in accordance with oilfield production status.By using new understandings of oil displacement efficiency,the remaining oil distribution of main oil reservoirs in Wenchang A oilfield was reestablished and good development efficiency was obtained.