Abstract: Cooling system is the key subsystem of CNC grinding machine. Its reliability has an important influence on the machining quality and efficiency of CNC grinding machine. Taking MKS series CNC grinder produced by Beier Machine Tool Works as the research object, the reliability of cooling system is analyzed. Firstly, the fault data collected were analyzed by FMECA, and the harm degree of cooling system to CNC grinding machine was calculated. Then the FTA analysis of the cooling system is carried out to find out the minimum cut set and the cause of the failure. In order to improve the reliability of CNC grinding machine, the corresponding solutions are put forward and applied to the actual improvement design.