Resistive random access memory (RRAM) based on electrochemical metallization (ECM) is a promising candidate for future nonvolatile memory applications. This paper discusses the resistive switching (RS) behavior and conduction mechanism in the ZrO2-based ECM nonvolatile memory devices. Whether Cu or Ni is used as the top electrode, two different types of I-V curves are found in the same device, representing different RESET modes. The I–V fitting analysis suggests that one RRAM cell can follow two significantly different conduction mechanisms under two types of RESET modes. Under sudden rupture mode, conduction at the high resistance state (HRS) is dominated by a space-charge-limited conduction (SCLC). In contrast, under slow dissolution mode, the devices at HRS tend to show an Ohmic conduction mechanism. These phenomena can be explained by a physical model based mainly on Joule heat or electric field, which is related to the degree of dissolution and rupture of multiple conductive filaments (CFs). Furthermore, the electrical field simulation results based on the solid electrolyte theory by MATLAB further demonstrate the coexistence of two conduction mechanisms in Cu (or Ni)/ZrO2/Pt devices HRS. This paper provides a direction for better understanding the conversion mechanism of ECM RRAM, which is of great significance for the further development of RRAM.