One-dimensional (1D) modeling is critical for turbomachinery unsteady performance prediction and system response assessment of internal combustion engines. This paper uses a novel 1D modeling (TURBODYNA) and proposes two additional features for the application to a twin-entry turbocharger turbine. Compared to single-entry turbines, twin-entry turbines enhance turbocharger transient response and reduce engine exhaust valve overlap periods. However, out-of-phase high-frequency pulsating pressure waves lead to an unsteady mixing process from the two flows and pose great challenges to traditional 1D modeling. The present work resolves the mixing problem by directly solving mass, momentum, and energy conservation equations during the mixing process instead of applying constant pressure assumption at the limb–rotor joint. Comparisons of TURBODYNA and an experimentally validated CFD suggest that TURBODYNA cannot only provide a very good agreement on turbine performance but also accurately capture unsteady features due to flow field inertial and pressure wave propagation. Levels of accuracy achieved by TURBODYNA have proved superior to traditional 1D modeling on turbine performance and the generality of the current 1D modeling has been explored by extending the application to other turbine featuring distinct characteristics.