For a certain type of graphite circumferential seal in service,the formula for calculating the contact load between seal ring of circumferential seal and mainshaft with radial runout was obtained,considering the radial runout characteristics of the circumferential seal.The ANSYS was utilized to analyze the influence of radial runout on stress and deformation under thermalstructure coupling.The results show that the stress and deformation of the seal ring are increased with increasing radial runout.When the radial runout exceeds 08 mm,the deformation is increased approximately linearly,and the stress increase gradient is significantly larger.The first 6 steps natural frequencies and modes of the seal ring were obtained by modal analysis,and the frequency response curves for stress and displacement were got by harmonic response analysis.The results of modal analysis show that the bending vibration,torsional vibration and swing of seal ring affect the working life of the circumferential spring and axial spring,and aggravate the fretting wear between the antirotation pin and the pin groove,and affect the followup characteristics of the circumferential seal.In combination harmonic response analysis with modal analysis,it is found that the resonant failure of the circumferential seal is prone to occur on the third,fourth and sixth orders natural frequencies.