This investigation attempts to consider the dynamics of cathode material microdroplets’ phase behaviour during vacuum-arc operation in the presence of passive working gas of argon. Using the multigrid electrostatic analyser technique, it is shown that both positively and negatively charged microparticles are present in plasma flows propagating from the cathode. The positive charge on microparticles is determined by their thermal emission. The evaporation intensity of freely flying droplets, which become positively charged, is mainly determined by both density and energy of ion flux on them and depends on the values of the plasma electron temperature in the discharge gap. For the calculation of drop evaporation rate, the value of explicit view of the energy distribution function for the singly and multiply charged ions in the flux along the trajectory of the drops, and initial values of the temperature and trajectories of microparticles, which leave cathode are required. Under very intensive energy flows on microdroplet, the presence of a gas—vapour target occurring around the drop during evaporation may cause a strong influence on the microdroplets’ evaporation rate.