As the oilfield development goes longer, the economic benefits generated by infill well become lower year by year. And the economic limit well pattern becomes the key factor for oilfield development decision making. Based on traditional well pattern calculation method, the well spacing and average well-controlled recoverable reserves of infill wells in 15 typical development units at different stages were studied, and the relationship between well spacing and well-controlled recoverable reserves were set up. Combining with the study of economic limit for well-controlled recoverable reserves, a new method to calculate the economic limit well pattern for old oilfields has been established. By using this new method to calculate the well pattern based on economic limit for No.2 district of Shengtuo oilfield under different oil prices, the results showed that it has potential for infill wells under high oil price, and the higher the oil price, the greater the potential for more infill wells.