Abstract: The heating of machine tool spindle is an important reason for the deviation of machining accuracy of CNC machine tool, so the water cooling design of machine tool spindle is very important. Based on computational fluid dynamics software FLUENT, the fluid solid thermal coupling of stator, water jacket and water cooling system of 170SD30-SY spindle is studied by finite volume method. RNG k-ε two equation turbulence model is adopted. The main shaft temperature rise of water cooling system under different process conditions is analyzed, and the design of water inlet and outlet pipes of water cooling system is reasonably optimized on this basis. The results show that the improved water cooling system can reduce the spindle temperature by more than 20 K, which provides a research direction for the development of similar products.