Abstract: Chaheji Oilfield is very typical complicated fault block reservoir,and Cha-39 is one of its main block.It has been developed for over twenty years.Therefore,its underground condition is becoming more complex,its development is becoming more difficult,and its economic benefit is becoming more poor.In order to improve development benefit,we must analyze the block once again,and find out the distributing rule of remaining oil.According to the actual state on reservoirs,utilizing the logs of boron neutron,dynamic analysis and reservoir simulation etc.,we synthetically study the distribution of remaining oil in Cha-39 block of Chaheji oilfield. It is pointed out that residual oil is relatively concentrated in faultage neighborhood,imperfect well netting position,and the place of low-grade channel sandstone and so on. Development measures which can improve development effect are put forward,such as adjusting injection-production system and increasing gross liquid yield.