The goal of the present study were (1) to investigate the pathological characteristics of gastrocnemius muscle (GM) and quantitatively assess GM tissue stiffness in rat models with spinal cord injury (SCI) and (2) to explore the correlation between pathological characteristics changes and Young's modulus value of GM. 24 Sprague Dawley male rats were allocated into normal control groups and SCI model subgroups, respectively. GM stiffness was assessed with shear wave sonoelastography technology. All GMs were further analyzed by pathological examinations. GM weights were decreased, the ratio of type I fibers was decreased, and the ratio of type II fibers was increased in the GM in the model group. MyHC-I was decreased, while MyHC-II was increased according to the electrophoretic analysis in model subgroups. The elastic modulus value of GM was increased in the model group. A significant negative correlation was found between Young's modulus value of GM and the ratio of type I fibers of GM in model subgroup. Our studies showed that the stiffness of GM is correlated with pathological characteristics during the initial stages of SCI in rats. We also identified shear wave sonoelastography technology as a useful tool to assess GM stiffness in SCI rat models.