As we know, thrusters are used more and more on engineering ship, which could improve the ship rotary mobility, but also increase the resistance. In this paper, the bow thrust tunnels of one ship have optimized by CFD simulations. At first, the CFD methods is validated and verified by the comparison with the experimental results of bare hull. Then different forms of bow thrust tunnel are designed, the optimization of the bow thrust tunnels have mainly considered the height and size, then we open diversion trench for the thrust tunnel, which could reduce the resistance well with proper direction and size. The model tests have carried out in CSSRC, results showed that numerical calculation and model test between optimization cases indicated similar resistance reduction.