Abstract: VSC-HVDC interfacetransformer is a bridge connecting AC and DC systems,the analysis of its fault characteristics is critical for protection scheme. However,when MMC of wind farm side（WFMMC）fault occurs in the VSC-HVDC interfacetransformer in double fed induction generators（DFIG）wind farms for voltage source converter based high voltage direct current（VSC-HVDC）transmission,the short-circuit current of DFIG side shows the characteristics of frequency offset and weak feed. The short-circuit current of WFMMC side not only contains a large amount of harmonic,but also amplitude difference,phase difference,and even disconnection under different control strategies. Such complex fault characteristics bring extremely high requirements and severe challenges to the appropriate operation of VSC-HVDC interfacetransformer differential protection. Therefore,this paper selects the most common singlephase grounding fault on the converter transformer WFMMC side for case studies,which analyzes the fault characteristics of shortcircuit current on the DFIG wind farms side and WFMMC side. Meanwhile,the reasons for the decline of differential protection performance is also discussed. On this basis,this work proposes a protection scheme to process the currents on both sides of the VSCHVDC interfacetransformer by using morphological filter decomposition and synchrosqueezed wavelet transforms. Besides,the internal or external faults are identified based on the slope of the current trajectory drawn by processed current. Finally,the simulation results based on PSCAD show that the proposed scheme can identify the faults and inrush currents rapidly and accurately,meanwhile,the scheme also shows good applicability under different influencing.