Abstract: The swirl brake is an important component to enhance the stability of the labyrinth seal. This paper calculated the influence of the swirl brakes on the pressure distribution, circumferential swirling flow, and rotordynamic characteristics in each seal cavity. The effectiveness of the swirl brakes was quantitatively analyzed and evaluated. Results show that the influence of the swirl brake clearance on the pressure in each cavity has an opposite trend for C₁ and C₂—C₉. The pressure in C₁ decreased with the decreasing swirl brake clearance, and the pressure in C₂—C₉ increased with the decreasing swirl brake clearance. The growth rate of the circumferential swirling flow was introduced to evaluate the influence range of the swirl brakes. The circumferential swirling flow growth rate for labyrinth seal with swirl brakes decreased along the leakage direction, and that for the no-brake labyrinth seal remained was basically kept unchanged. As the clearance of the swirl brake decreased, the influence range of the swirl brake on the circumferential flow increased. The reduction of the swirl brake clearance increased the cross-coupled stiffness in C₁ and decreased the cross-coupled stiffness in C₂—C₉. The effective damping and the system stability could be improved. The increase of the preswirl ratio increased the cross-coupled stiffness in C₂—C₉, which is easy to cause the seal instability.