Direct numerical simulation is performed to investigate the connection between the evolution of the turbulent/non-turbulent interface (TNTI) and the entrainment and detrainment process in a temporally evolving turbulent plane jet with Taylor Reynolds number of about \(Re_\lambda \approx 72\) . For an accurate calculation of the surface area of the turbulent interface, a novel algorithm is used. On average, the stretching term and the curvature/propagation term counterbalance each other, maintaining a constant surface area of the TNTI. We show that regardless of the entrainment or detrainment process, the stretching term always contributes to the production of surface area. The curvature/propagation term contributes to the destruction of surface area in the entrainment process. In contrast, the curvature/propagation term is related to the production of surface area in the detrainment process.