Abstract: Well spacing density is an important index when planning oil field development and network design. A method for computing limited well spacing density and reasonable well spacing density after several years' production of water flooding oilfield has been presented, based on the previous methods as well as economic evaluation parameters for the maximum economic benefits. This method not only considers the time value of capital, investigation, costs, taxes and rate of crude oil products, but also includes the production decline rate. This method can provide a reference for computing well spacing density in waterflooding oilfield.