Abstract: The strategy of fewer wells and higher production is preferred in offshore oilfields because of the high cost. Interference between layers is becoming a great problem while water flooding in fluvial facies oilfields, which have multi–layers, thinner thickness and serious heterogeneity. Practice indicates that separated layer water injection and deployment can only temporarily relieve the problem. Facing this problem, there needs to be a new way to increase production. Taking block 4 of M oilfield in Bohai as an example, separate strata and optimizing fracturing reservoir are proposed through studying the current block flooded condition and remaining oil distribution, which has got a higher EOR with the guarantee of single well productivity. The results indicate that separate strata can increase EOR by 1.8% and cumulative oil production by 12.7×10~3 t. Separate strata and fracturing are carried out in M17 well, which has increased daily oil production by 50 m~3, achieving the desired output effect.