In transient computational fluid dynamics (CFD) simulations, the continuity of the flow field is an essential prerequisite. However, continuous flows can be separated under certain conditions, such as the process from valve opening to reclosure. The current method often leaves a narrow gap to estimate the full closing status, which will introduce a deviation. To address this issue, a full closing numerical simulation method (FCNSM) is developed to solve the problem of simulation between discontinuous flow field (DFF) and continuous flow field (CFF). The matrix laboratory (matlab) program has been used to communicate fluent as a server session to call the files fluent and automatically execute text-based user interface (TUI) commands. The radial basis function (RBF) is used to construct the relationship between the variables of the flow field and the coordinates of mesh nodes, which can achieve the data transmission from a DFF to a CFF. Automatic stopping of transient calculations is achieved by passing variables among matlab program, scheme language, and user-defined functions (UDF) when a physical quantity reaches a set value. Based on this method, a transient simulation with a dynamic mesh of a 2-D model regarding a pressure relief valve (PRV) is performed to simulate the process of the valve from full closing to reclosure, the flow characteristics through the PRV are obtained using this method. This study makes it possible to use FCNSM for understanding dynamic characteristics from DFF to CFF.