Freeze valve is one of the major safety systems used in the Molten Salt Reactor (MSR), that automatically opens in case of accident. The freeze valve was first developed in the Oak Ridge National Laboratory (ORNL) to be utilized in the Molten Salt Reactor Experiment (MSRE). Currently, many organizations have developed different types of MSR. Thus, appropriate freeze valve designs are needed. Fundamental studies to understand the basic features of freeze valve are important to develop new designs. The purpose of this study is to analyze the effect of convection in the molten salt on the opening time of the freeze valve. Numerical simulations were conducted using the ANSYS Fluent 18.1 and the results were compared with the experimental data obtained under similar conditions. From the calculation results, it was found that the convection in molten salt is often neglected but it noticeably accelerate the opening time of the freeze valve. It was concluded that the convection effect should be taken into consideration in the design of high-performance freeze valve.