Abstract: In this paper, the current specification concerning strength computing theory of shaft bracket is analyzed, and it is seen that structural stiffness coupling is not considered in this theory. In the view of the shaft bracket structural and mechanical features, the reaction force model of shaft brackets considering structural stiffness coupling is established, and the calculation formulas for the internal forces of the shaft brackets are derived, and the parameters of the generalized stiffness ratio describing the structure stiffness coupling effects is defined. Taking shaft brackets of a certain boat as an example, the quantitative calculation on FEM simulation, the computing theory presented in this paper, and the conventional computing theory without considering structural stiffness coupling are applied, respectively. In addition, the computing method on torsional rigidity of shaft brackets is also put forward. The results show that the computing theory of this paper agrees well with the FEM simulation, while the conventional theory deviates far from the FEM simulation performance. Moreover, the conventional theory yields larger result, which further worsens with the enlargement of the generalized stiffness ratio, causing the overly design of the shaft bracket structure strength. In brief, the computing theory proposed in this paper serves as great guidance to the optimization in the strength design of the shaft bracket structure.