The resistive switching (RS) behavior of resistive random access memory (RRAM) based on oxygen vacancy (V _O) conduction is significantly affected by the interface properties between metal electrode and oxide layer, yet the modulation between the RS behavior and the physico-chemical properties of the interface is still not very clear. In this study, the correlative role of Ta/HfO ₂ interface with the RS behavior in HfO ₂-based RRAM is explored at atomic level. First-principles thermodynamic calculations show that the strong interaction between three-fold oxygen vacancies (V _O3) leads to a formation of V _O3-based conductive filament (CF) along direction perpendicular to the interface. Four-fold oxygen vacancies (V _O4) make a major contribution to the re-formation and growth of CFs during the set process by diffusing into the residual filaments. The results of electronic properties further indicate that as the number of V _Os perpendicular to the interface increases, the charge redistribution between O and Ta atoms at the interface is significantly increased, and more electron clouds are gathered around V _Os. This is the underlying mechanism of forming a conductive channel. This study reveals the important regulation mechanism of the interface characteristics between metal electrode and oxide layer in RRAM on the formation and growth of V _O-based CFs.