Abstract: Most wells are completed and treated through a packer,to determine correct location of packer,compensating value of axial displacement of tubing string and whether the packer is leak while the gas injection at various working conditions.In consideration of piston effect,helical effect,pressure and temperature change effect,relaxation forces effect and friction effect of the fluid in the tubing string by elastic mechanics,and analyzed the stress and displacement of the tubing string,calculated axial extension of string under influence of different factors.The result shows that there have obvious influence on axial displacement of string considering transverse pressure effect compared with general method in gas injection wells,and the axial extension of string caused by fluid flowing is proportional to the square of the velocity of gas injection,the velocity of gas injection has a obvious influence,and axial displacement grads increased greatly in high injection pressure.