With the rapid development of electronic devices for more compact structure and rapidity speed, the traditional single-phase radiator cannot meet the demand of an increasing heat flux from the electronic components. The effects of inlet Reynolds number on the evaporative heat transfer of CO2 in a loop heat pipe evaporator are numerically investigated in this paper. The objective is to seek an achievable approach to enhance the heat-dissipating efficiency and provide a low operating temperature for the electronic components. The temperature of the bottom oscillates continuously during the evaporation process and is influenced by the vapor; the pattern of two-phase flow is quite different from single-phase flow. It is also found that the heat transfer coefficient of CO2 increases with the inlet Reynolds number largely.