Abstract: Oil displacement by CO₂ injection is an important measure to enhance tertiary oil recovery,and it is very important to monitor and evaluate reservoir performance pre-and post-oil displacement.However,there is't a series of matured performance monitoring and evaluating techniques for oil displacement by CO₂ injection at home or abroadyet.Pilot tests of CO₂ miscible displacement have been carried out in Et formation reservoir of CS Oilfield in Qingtong Depression of the Subei Basin.Through combination of performance monitoring techniques(such as interwell trace,well test,water and gas injection profile,produced fluid profile,remaining oil saturation,and properties of oil,gas and water) and relevant monitoring techniques,it meets the requirements of low permeability oil reservoir in complex fault block to prepare testing program for CO₂ miscible displacement,optimize and adjust test parameters and evaluate the effects.