The twin-screw ship with shaft brackets has been calculated by using the CFD software NUMECA\FineMarine, the resistance increments of the bow thrust tunnel, shaft bossing and shaft brackets at the different scales are calculated, the scale effect of the appendage resistance, wave pattern and the wake of the hull with shaft-brackets are analyzed. The results show that it is feasible to study the scale effect of the twin-screw ship with shaft-brackets by changing the length of the model based on CFD methods. Since the local Reynolds number of the appendage region is much smaller than the hull Reynolds number, the resistance increments of the three appendages become stable when the hull Reynolds number is larger than 10 ⁸. The Reynolds number for the model test of the twin-screw ship with shaft-brackets should be as large as possible in order to reduce the influence of the scale effect.