Abstract: In light of the problem that currently on the spot there is no way to effectively verify the sealing performance of the middle and lower packers of the multi-stage blocking pipe string, a new type of sealing detector was developed to check the sealing performance of the multi-stage hydraulic or mechanical setting packer. The sealing detector was connected to the lower side of the packer who need to be checked, the packer was set first and then the sealing detection channel was opened by increase pressure. After setting the sealing detector and stopping the pump, the goal packer was checked to verify the sealing performance. So far 3 wells have been treated in the oilfield, and the success ratio of operation and the effectiveness are all 100 percent.