In this paper, the long-pulse output characteristics of a mid-infrared solid-state laser based on different Fe²⁺∶ZnSe crystal samples are investigated. An Er∶YAG pulse laser with a maximum single-pulse energy of 600 mJ is utilized as the pump source, and the crystal is cooled in a vacuum chamber with liquid nitrogen. A long-pulse output with a maximum energy of 184.4 mJ and a pulse width of 1 ms, corresponding to a slope efficiency of 45.5%, is achieved on a 6 mm thickness coated sample at 85 K. For the uncoated sample, the output characteristics are compared at different fixed angles of the sample, and the results show that the output efficiency is higher when appropriately tilted.