For a metal hydride (MH) reactor, the thermal managements (e.g. expanded fin) are indispensable for improving the heat transfer between the MH bed and environment. The performance of a specific thermal management is often analyzed and optimized using high fidelity models (HFMs), which can capture the physical field evolution accurately. However, the thermal management analysis from a system point of view, which is of great importance for the integrated system design, can hardly be done using HFM due to the high computational cost. In this paper, a new reduced model (RM) of MH tank is firstly established based on the state-space model with two correction matrices. The model has been proven to provide satisfactory accuracy compared with two-dimensional model and capable for the prediction of state variables under different geometry parameters of fin. What's more, the effect of geometry parameters of fins on the dominant pole are also analyzed, and the results indicate that the evolution of dominant pole can reflect the effect of both heat transfer and hydrogen storage capacity on the dynamic characteristic of MH tank, contributing to the thermal management optimization.