Abstract: In deep formation light oil. condensed gas and natural gas are often berried，forming special oil and gas reservoirs of high economic value. Under high pressure and high temperature, liquid hydrocarbon is disolved in gaseous hydrocarbon. When pressure drops below bubble point, the retrograde condensation phenominon occurs in reservoir fluid，resulting in gas retrograde condensate remaining in the reservoir. Therefore,the miscible nitrogen injection is practiced abroad for effectively developing light oil reservoirs. With the pressure increased in condensate reservoirs. high recovery is obtained. There are two kinds of miscible displacement. One of them is multi plecontact miscible displacement, being also called dynamic miscible displacement. which is completed by multiple distillation and extract. The example of miscible nitrogen injection in Fordoche oil field, U. S, A. is given in this paper . the predicted ultimate recovery is as high as 54.5%. Finally， some suggestions are made on the effective development of condensate gas and volatile oil fields.