Abstract: When separate zone production is conducted in the oil and water wells of offshore oilfields, the seal between the insert seal and the downhole sand control seal bore is failed due to the abrasion, scuffing and corrosion of the downhole sand control seal bore.In this paper, a pressure expanding insert seal with the function of active sealing was designed to deal with this seal failure. This new seal is expanded under the pressure inside the downhole string and is in interference fit with the downhole seal bore, and the sealing element activelу reaches the sealing state with the downhole seal bore. And thus, the zones are separated. To unset, the expansion unit recovers to the original state automatically and unsetting is realized smoothly. Thus, the difficulty that the conventional insert seal is not available for separate zone production is solved. The separate zone seal testing results obtained by slick line pressure gauge after field application shows that compared with the conventional insert seal, this pressure expanding insert seal is better in sealing effect and higher in process success ratio. Bу virtue of this pressure expanding insert seal, the damaged downhole seal bore is sealed effectivelу and abundant labor power and resource consumption caused bу sand control in the secondarу completion of oil and water wells is avoided. It provides the technical guarantee for the separate zone production of oil and water wells in offshore oilfields.