The Hall plot method, proposed by Howard Hall in the 1960s, is a widely-used tool for analyzing injectivity. Over the past decades, industry has been modifying the Hall plot method for applications in various scenarios such as formation damage and/or stimulation diagnosis, polymer injection, and gas injection. It has proved to be a simple, inexpensive, and effective way to diagnose changes in injectivity. However, such applications are limited to vertical wells. This study proposes a new formulation of the Hall plot method for analyzing horizontal well injectivity. A numerical simulation model was built in CMG to verify the proposed method. The Hall plot method for horizontal well was then used to study various scenarios with different extents of formation damage, numbers of damaged skin zones, and reservoir anisotropy conditions. The works carried out in this study confirm the applicability of the Hall plot method on analyzing horizontal well injectivity