Through the statistics of the permeability,the author again recognizes and classifies the main layer and non-main layer of the north block in the Baolang oilfield.The author uses the advanced constant-rate intruding mercury technology and nuclear magnetic resonance technology to evaluate and classify again the reservoirs in the north block.The author uses the nuclear magnetic resonance technology to research the water drive efficiency and the movable extent of the fluid in different pores.In the micro-economic theory,the author researches and explains the low recovery degree of big pores and the high recovery degree of small pores in the low permeable cores,and the high recovery degree of big pores and the low recovery degree of small pores in the high permeable cores.