<p>The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways. The elastic-plastic analytical solution for surrounding rock was derived based on unified strength theory. A model for solving the stress gradient of the surrounding rock with the intermediate principal stress parameter <i>b</i> was established. The correctness and applicability of the solution for the stress gradient in the roadway surrounding rock was verified via multiple methods. Furthermore, the laws of stress, displacement, and the plastic zone of the surrounding rock with different <i>b</i> values and prestresses were revealed. As <i>b</i> increases, the stress gradient in the plastic zone increases, and the displacement and plastic zone radius decrease. As the prestress increases, the peak stress shifts toward the sidewalls, and the stress and stress gradient increments decrease. In addition, the displacement increment and plastic zone increment were proposed to characterize the support effect. The balance point of the plastic zone area appears before that of the displacement zone. The relationship between the stress gradient compensation coefficient and the prestress is obtained. This study provides a research method and idea for determining the reasonable prestress of support in roadways.</p>