Annular seals are the key component of turbomachines to reduce the fluid leakage.The fluid-induced vibration characteristics of the annular seal are extremely crucial to the system stability.Based on the computational fluid dynamics method and a multiple frequencies whirling model, the fluid-induced vibration characteristics of an anti-stagnant labyrinth seal were investigated.The effect of anti-stagnant nozzles’geometry parameters and its position on the dynamic and static characteristics was studied.The fluid-induced vibration suppression mechanism of the anti-stagnant nozzles was examined.The results show that the anti-stagnant flow can significantly suppress the circumferential flow, and improve the pressure distribution on seal cavities and the system stability.Compared with the traditional labyrinth seal, the anti-stagnant labyrinth seal possesses a smaller cross-coupled stiffness coefficient k, a larger direct damping coefficient C and an effective damping coefficient Ceff.The suppression effect on the unstable vibration is especially remarkable at low frequencies.There exists an optimal radial position for the anti-stagnant nozzle with identical geometric parameters.When the centroid height hc is 1.65 mm, the effective damping Ceff is the largest.Increasing the nozzle inlet height hin and decreasing the ratio of outlet/inlet height hout/hin can both improve the system stability.The anti-stagnant labyrinth seal with hin=1.00 mm, hout/hin=0.25, hc=1.65 mm, is the optimal structure for the current calculation conditions, while the leakage flowrate increases slightly.