Based on the best track data from China Meteorological Agency and 6-h reanalysis data with a resolution of 1°×1° from National Centers for Environmental Prediction,this study conducts the piecewise potential vorticity inversion to reveal the dynamic mechanism by which the 15th super typhoon Goni in 2015 suddenly changed its track.The results are as follows.(1) From the perspective of synoptic system,Goni was affected by the large-scale background system and the steering flows including the Northwest Pacific subtropical high,the monsoon gyre,the typhoon Atsani and the peripheral anticyclone of Atsani during the whole lifetime of Goni.(2) On the basis of quantitative analysis of the steering flow inverted from potential vorticity perturbation associated with the four components,we find that the steering flow vector of Goni was always affected by the Northwest Pacific subtropical high,while the monsoon gyre and peripheral anticyclone played a secondary role.At the time when Goni turned northward suddenly,the steering flow associated with the peripheral anticyclone acted as a major factor that resulted in the abrupt northward turning.(3) The contribution of the total potential vorticity perturbation to the relevant steering flow at different altitudes is further analyzed quantitatively.Results show that the steering flow vector in the middle troposphere is in good agreement with the movement of Goni,and the southerly flow formed in the low-level system is closely related to Goni's abrupt northward turning and its subsequent enhancement in the upper troposphere after the abrupt turning.