Mechano-electrochemical milling (MECM) is a promising method to machine TC4 titanium alloy as it combines electrochemical machining (ECM) and conventional milling (CM). However, prior studies on the interaction between ECM and CM are few, lacking in-depth understanding of the material removal behavior of MECM. Therefore, the interaction between ECM and CM of TC4 titanium alloy was experimentally investigated in this paper. Experimental results showed that the initial CM surface obtained lower surface impedance and corrosion resistance compared to initial normal non-CM surface, which reduced the breakdown potential of surface layer and improved the current efficiency of TC4 titanium alloy. During electrochemical dissolution, the initial CM surface dissolved mainly first from the junction of the adjacent tooth marks, then the dissolution diffused gradually to the center of the tooth mark resulting in large-scale local dissolution until all the initial tooth marks were completely removed. In addition, the initial ECM surface had lower surface microhardness compared to the initial CM surface. This decreased the milling force in the subsequent CM, which might be conducive to reducing tool wear and prolonging tool life.