Model GMN expansion joint is a key accessory to downhole string, which is used for compensation mechanism by the length change of string that caused by internal and external pressure or temperature changes mechanism. So that to avoid the danger of excessive axial load changes. It can be used with mechanical or hydraulic packers, and is widely used in fracturing, acidizing and other stimulation measures, and is also widely used in water injection and gas injection. GMN type expansion joint can maintain the pressure in the oil pipe and ensure its safe expansion and contraction. The SEJ type expansion joint can transmit torque, and the expansion joint can be placed on the upper part of the packer or in the middle of the two-stage packer according to the specific situation.