The well pattern and well spacing are the basis for the formation of an effective injection-production relationship in the oilfield,and also the key directly affecting the oil recovery rate, the size of the investment and the economic benefits.Therefore, the rationality of the well pattern is an extremely important part of the design of oilfield development plans,particularly for offshore oilfields with sparse well pattern and large well spacing.On the basis of empirical formula of the institute of petroleum exploration and development, a new formula between recovery factor and well pattern density was established respectively by introducing the oil displacement efficiency of actual oilfields, proposing the method of characterizing the replacement ratio to determine the well density by using the ratio of the production capacity between horizontal wells and vertical wells, and using the method of calculating well pattern factor.On the other side, the rationality of oilfields well pattern is studied by combining the economic evaluation model of offshore oilfields.The case study shows that the method is highly applicable and can well reflect the relationship between recovery factor and well pattern density, which can provide a basis for oilfield encryption adjustment.